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tylerw02
01-03-2008, 05:49 PM
It is possible to agg better at 200 or 300 than 100, simply because of the way MOA works. However, is it possible to have a smaller extreme spread at extended ranges than at 100 and why or why not?

Just looking for some ideas...this topic came up in another forum recently.

J. Valentine
01-04-2008, 12:44 AM
Not sure what you mean about the whole MOA thing.
However it is possible to have a rifle /cartridge / load combination that exibits less spread at longer range than short range on a MOA basis .
The old British SMLE had beter accuracy at 1000 than 100 on a MOA basis.
It was called Positive Compensation or Flip.
Something to do with how the barrel acted that brought the bullets closer together at long range.
Mauser style actions dont seem to do it thank god.

HovisKM
01-04-2008, 07:47 AM
yes, you can shoot a smaller MOA at 200 or 300yds than at 100yds but that is not the norm. I have one rifle that seems to shoot the same group at 200 as it does 100yds, the only problem is the 200yd groups are good but the 100yd ones leave a lot to be desired. As far as extreme spread goes (assuming that you are talking about velocity), you can not shoot a smaller extreme spread at longer ranges than you can at shorter, they will be the same. Just think about it, are bullets going to adjust their velocity closer to one another once they are already on their way? Just can't happen.

Hovis

jackie schmidt
01-04-2008, 10:47 AM
I don't know about this thing where there are claims that bullets somehow find their way back together out at longer ranges. This defies the laws of physics. Once an object is headed in a certain direction, something has to act upon it to make it change direction.
It would seem that once the bullet is started off on a different course than the one before, (this starts with internal ballistics and ends the moment the bullet exits the muzzle), something would have to affect it to make it go back on the intended course.
We all know that conditions move bullets around. But I doubt there are any internal homing devices that cause bullets to hone in on a certain point.
As for the MOA thing, yes, in really good conditions, it is not uncommon for Competitors to shoot better aggs at 100 than 200. But normally, conditions dictate the aggs, and things are usually bigger at 200, when speaking in terms of MOA.
........jackie

tylerw02
01-04-2008, 11:26 AM
I used the wrong word with extreme spread....I'm meaning the actually measurement of the group, rather than MOA.

Jackie, you're reflecting what I'm suggesting on the other forum, unless there is some form of seeker bullet, I cannot think of anything to suggest it could physically happen.

Repeatedly I've heard people suggest their rifle "shoots a smaller group" at 200 than 100. To deny the feasibility opens the door for a shady physics "lesson."

My simple explanation: "had that group been shot at 100 rather than 200, it would have been better and that bad 100 yard group would have been even bigger at 200."

WalkerTXRanger
01-04-2008, 11:34 AM
I think what commonly happens is this, they fire a group at 100 yards that is 1 inch, then their group at 200 yards is 1.5 inches, then they are saying their rifle shoots better at 200 yards than 100 yards.

Bnhpr
01-04-2008, 12:36 PM
From a scientific standpoint, what Jackie said is correct. It appears this phenomena belongs in the list of ballistic urban legends. If someone shoots better at 200 meters, vs 100, they just shot a better group.

Assuming the bullet trajectory is straight, it is, as Jackie says impossible for an object to redirect without an external force. If wind were redirecting, the wind would have to change every shot, and move it the desired distance and direction. This is, however not impossible, but extremely improbable.

Assuming the bullet trajectory is curved (besides gravity), every bullet would have to curve in the same converging direction. this, again, is extremely improbable.

So, I'll refer to the second law of thermodynamics in reference to the question. In summary, energy moves from a higher state to a lower state, and in this instance from order to disorder.

The other one I've heard claims of, is a bullet is hight at 100, low at 200 and high again, at 250. Not likely.

HuskerP7M8
01-04-2008, 01:14 PM
Here's an interesting theory on this subject.

http://www.the-long-family.com/bullet_dispersions.htm

Landy

Bnhpr
01-04-2008, 01:29 PM
Good topic for myth busters

stevelong
01-04-2008, 02:07 PM
Hello, I'm not a true BR guy, but I dabble in some accuracy shooting, and compete in 200 & 1000 yard matches. I mean, I don't have tons of experience & knowledge, like a lot of the posters do.
BUT, I can unequivocally say that I have a trued 700 6br 8-twist Krieger rifle that will absolutely not ever shoot 1's, 2's, or 3's at 100, but I have (on several occasions, often enough to show it's probably not just a good day - I don't have those) shot the same 100 yard load & several different loads into 5 shot groups at 500 yards going 1.3", 1.1"......and the like.
SO I'm not scientific enough to answer the question, but my 2 situations are repeatable enough that I think it's not the random, bizarre, low percent "chance" that it can't be a reasonable theory.
I thought I've read on this forum maybe a couple years ago that there are some scientific minds far better than mine that say that it absolutely does happen, a rifle and load shoot an inch at 100 & far less than 5 inches at 500, etc.
I know, it doesn't make "sense", and I know, everything MUST follow a rule.
But there are some "rules" that we sometimes just don't ? get.....
??
Steve Long.

alinwa
01-04-2008, 02:25 PM
Ok, coupla' things...........


Mythbusters is 'WAYYYY out of their depth on this one ;) so they ain't any help.......



But so is this guy on the aforementioned website.


To anyone who really DOES understand how a bullet flies THIS >>>> " this upward twist force or torque will result in the nose of the bullet yawing to the right. This yaw is called the "yaw of repose". This yaw in turn causes the bullet to steer a bit to the right (following the nose)." <<<< STATEMENT shows his ignorance of the subject.


A bullet does not "follow it's nose" and until folks can visualize this then "wind drift" and "aerodynamic drift" and "the fact that bullets drift HIGH to the left and LOW to the right" (sometimes termed "wind drift induced vertical dispersion) will be a mystery. Everyone seems to think that bullets fly on planing surfaces like airplanes and they DON'T!


Dude is 180degrees off in his analysis (actually only 178* off but who's quibbling ;) ) and is also completely wrong regarding decreasing MOA with range..............If he thinks that the difference he points out regarding inch group sizes and moa groupsizes is "subtle" then he really needs work on his social skills.



In short, the guy on the website listed, Chris Long, is full of hot air, he's right up there with the Nennsteil Rupprecht (sic, don' wanna' bother) website about "how bullets fly" for propagating low-grade highspeak mumbo jumbo.


Mayhap someone can prove me wrong??? I do have McCoy's book close to hand for reference so if anyone cares to ref Chapter 11 sect. 4 and walk me through how it "clearly support's" Dude's contention I'm game :)



LOL




al



Ohhh Yeahhh, Tylerw02, lissen to Jackie, he's the real deal.





Now, do folks regularly SHOOT smaller groups at longer range???


ABSOLUTELY!


In fact nearly every competitive bow or pistol shooter will confirm this, I'd 'WAYY rather compete at 50yds with my bow VS 15 or 20yds, I'll shoot smaller at 50 yards 9 times out of 10. This is in no way "mysterious".

Charles E
01-04-2008, 04:11 PM
Consider this: A bullet orients its point into the center of resistance. So, if there is a crosswind, the bullet will point a bit into that wind, and the accompanying drag will be so oriented, & move the bullet "downwind."

OK, consider this model:

For the first 100 yards, there is a 10-mph crosswind. The bullet orients its point into the wind, and drifts as you would expect. After the bullet has gone 100 yards (in the crosswind), either the wind stops, or the bullet is shielded from it for the next 200 yards. It will re-orient its point straight down range. This happens in about 1 revolution of the bullet, i.e., quickly. Nothing will change the dispersion from the wind already there, but no further (wind) dispersion will be added. So on this model, in terms of MOA, it seems that yes, the MOA at 100 can be greater than the MOA at 300. Nothing to do with the rifle or bullet, just the wind.

Reasonably unlikely scenario, though.

Cheechako
01-04-2008, 04:18 PM
Oh, not again! It's only January and it's come up already. This subject has had more threads on the shooting Forums than "moly vs naked" and "will a 45-70 kill a deer".:rolleyes:

For those who believe that it's possible, do this simple test and report back. Set up two targets, one at 100 yards and one at 200, 300, whatever. Line them up so that your group will pass through both targets. Shoot a 5-shot group under good average conditions. Compare the group sizes and post your results here for all to see.

Ray

J. Valentine
01-04-2008, 05:02 PM
Jackie , It seems odd to me also but the English say it did happen with the old Lee Enfield SMLE and Im sure it was also reported in Precision Shooter years ago .
I heard about it much before that .
There was a guy in Australia I think , that had a special flexible bedding system for the " muzzel end " called a " Dean Floater " That capitalised on this trait. We don't know everything and lots of unusual things have been lost in time . The English say it was the reason that they were so hard to beat at fullbore prone at 1000 yards in those days.
Thats what the history books say anyway , so go figure . I have not seen it with my own eyes however.

Gerry
01-04-2008, 05:57 PM
Humm interesting'
Here's my Opinion via observation.
I had a barrel that shot consistently small at 200 yd and very small at 300
At 100 it also was just so so. The long pointy 8 3/4 ogive bullets were the answer. They weren't quite as stable at 100 yds. i changed to a 7 1/2 for 100 and 200 and the groups shrunk. when i shot out to 300 i went back to the point 8 #/4 ogives and shot an official screamer at that range.
I don't believe the pointy bullet was quite stable at 100. it was fine at 2 and 300/ i believe it's bullet shape that causing the problem. i would try different shaped bullets and see what happens.

alinwa
01-05-2008, 02:55 AM
Charles E,


I don't see your bullet "re-orienting it's point straight down range" but instead "re-orienting it's point on the center of it's (new) flightpath."

Am I missing something?


In other words, even if you back off from the tunnel mouth and shoot thru 100yds of exterior conditions into dead air you cannot do better than to MAINTAIN the dispersion induced by the conditions. Nothing can induce bullets to magically converge except sometimes the aforementioned "Flip" and then only on the vertical plane, just like a quarterback throwing two passes to the same receiver.....one of them a "bullet" and one a "lob"..........they both hit their target but only at one given yardage, after that the trajectories cross over and their measured dispersion rate is actually GREATER than before.


This is an illusion only, the true vertical dispersion is masked or compensated for by the muzzle "flip".


I guess variable crosswind and luck COULD as you say produce the same effect on the horizontal if you were a hind-feet weather vane shooter.....ya' just makes sure to shoot your slow rounds in the lulls!



LOL



al

J. Valentine
01-05-2008, 05:19 AM
It hurts to say this but Alinwa has struck a good point.
The only yardage they used the Lee Enfield rifles at was 1000 yds. only.
Then switched to Mauser actioned rifles for other distances.
It beats the hell out of me.

Charles E
01-05-2008, 08:24 AM
In other words, even if you back off from the tunnel mouth and shoot thru 100yds of exterior conditions into dead air you cannot do better than to MAINTAIN the dispersion induced by the conditions.

What I'm saying is, yes, the amount of dispersion already in the flight will be maintained, but will not increase. So, if the bullet has "dispersed" one inch at 100 yards, it will be 1 inch at 200 yards, not two inches. That would be a reduction in MOA, though not in inches.

I could be wrong, but here is my thinking. We learned in high school physics that once a vector is established, it will take work to change that vector. The usual (& erroneous) understanding of wind is that is "pushes" the bullet, so on the erroneous model, if the wind stops, the force stops, and the bullet continues along that vector.

I think this is the basis for most people claiming that a wind near the muzzle has more effect on a bullet than a wind downrange.

What I'm suggesting is that's not a good model, but I could be wrong.

The reason it's not a good model is because the wind doesn't "push" a bullet. Drag "pushes" a bullet; wind just orients the drag. When the wind quits, the drag is still there -- the force applied to the bullet doesn't change, in other words, only its direction -- work is still being done.

So, if the range lies due north, and for the first 100 yards there is a west wind, the bullet will point a little bit westward, and dispersion will be eastwards. If the wind quits at 100 yards, the force (drag) acting on the bullet does change direction, and the bullet will point downrange (due north). There will be no change in the amplitude of the force, but there will be a change in its direction. So yes, there is a force acting to change the vector of the bullet.

The problem in this is that a bullet goes 100 yards in about .1 second. For the air mass to stop moving the next .001 seconds (about a yard) is just not going to happen; the air (wind) too has inertia. Maybe your example with the tunnel would show this.

What am I missing?

Jim Mullican
01-05-2008, 08:42 AM
Gravity ?

Dave Short
01-05-2008, 09:15 AM
Conclusions, observations........

*Once a bullet leaves the barrel, it is on its own...there is no magical force that will cause the bullet to do what you want it to do.

*Once a bullet departs from its intended path, the best case scenario is that it will continue on its new path (vector). The further down range the bullet goes, the greater the distance between the intended and actual paths becomes.

*There are a number of forces that effect the bullet's path. The further down range it goes, the more of these forces it encounters.....therefore, it is less likely it will stay on course.

And........Some of us probably are more careful or try harder at 200 & 300.

Soooo.........

*Fortunately, every shooter on the line at a given match has to deal with the same conditions and variables...........the only real exception is range position, which is usually of considerable significance...

-Dave-:)

GARMASTERS
01-05-2008, 10:36 AM
In all the time we've spent reading all this think of how much ammo we could have reloaded!

Gerry
01-05-2008, 12:04 PM
Humm i guess you just don't get it Stability. aka bullet wobble.
The pointy bullet didn't settle in till 200 simple'

Charles E
01-05-2008, 02:05 PM
Humm i guess you just don't get it Stability. aka bullet wobble.
The pointy bullet didn't settle in till 200 simple'Right. I don't get "Tinkerbell did it" explanations either. How does "bullet wobble" (aka coning motion) explain shot dispersion? & for that matter, how does a bullet taking a nap get back on course? If you're going to ignore theory -- which is just fine -- you gotta do the two targets, one shot approach, to get empirical evidence that the model of the theory is wrong.

Gerry
01-05-2008, 03:33 PM
You still don't get it"
ask speedy. to bad miles hollister isn't around or ed Watson.
It would be really interesting . The gyroscopic forces and twist ratio
Is the factor . it's been around for a long time. The bullets are quite stable at 100 as the velocity decreases at 200 the wobble straightens out. . I'm talking short range group. Now take into consideration the long range factor. low drag bullets do very well , hence the vld. That aside. flat base bullets also do better at the short ranges. that boat tail doesn't kick in for quite a while.
i once asked Miles about making me some really good boat tails. his answer was OK .
But you'll need an exceptional barrel to stabilize them. That's what i know and have seen happen.
take it or leave it.

Boyd Allen
01-05-2008, 04:09 PM
The reason that these discussions seem to go on forever and get nowhere is that there are a whole lot more theorys than verifiable facts. If there were more facts, more difinitive proof, one could point to it and end the discussion.

About the best that we can do is to say that "I did such and such, and this is what happened." From that point it is up to others to verify the results by doing the same thing to see if they get the same result.

As far as real proof goes, none of is have the time, resources, and I suspect, singlemindedness. What we are left with is endless posts defending each of our imaginings and/or interperatation of what someone else has written. It would be nice if all the written sources agreed, but alas, if I remember the last time this came up correctly, that is not the case. Understand that I am not discouraged by all of this. It is winter after all, and one has to keep busy somehow, when the weather keeps us indoors. Carry on.

Charles E
01-05-2008, 04:44 PM
No, both the army and the NRA have done tests. They shot through multiple targets, so each shot printed on each target at different distances. Horizontal dispersion was constant in terms of MOA, vertical dispersion greater (again MOA) with distance, but within the amount of vertical you would expect given the velocity variations (this last was stated by the army, not me).

For people to come along & say the US Army & NRA are wrong, they need to show it. Not just "I shot so&so one day at 100 and such&such later at 200."

No ballistic theory I know of -- & this would include the years of testing by the Army at Aberdeen, uses the term "goes to sleep" or attributes increases in shot dispersion to small levels, say the difference between 4.5 degrees and 3.5 degrees, of coning motion. Moreover, coning motion is the sum of the fast arm and the slow arm; the fast arm damps, the slow arm grow slowly. Different rates of twist get you different amounts of fast & slow precession, but the sum varies only about a half to one degree.

We should keep an open mind, but what counts is constantly repeatable tests -- and the US Army has done a bunch of these. If you think brenchrest is demanding, consider the needs of artillery at 6000 yards.

alinwa
01-05-2008, 04:45 PM
Charles,


To answer your first question, what you're missing is that dispersion is angular, originating from a point, not linear, trying to travel parallel to a line. A dispersion of 1" at 100yds is automatically at least 2" at 200, 3" at 300 and se ........... lines originating from a point (your barrel) and diverging (showing dispersion) cannot somehow begin to CONverge as they get further from their point of origin.


Regarding the effect of a bump at the muzzle being of greater effect than a bump further down.......this is true. Regardless of bullet orientation, regardless that the bullet is "sucked" offline instead of "bumped" offline, its path is still reset. A "bump" from the wind is no different than a "tick" off the edge of a baseball bat or a bounce off the rail on a pool table.............a NEW flight vector is established, the bullet "ricochets" in the air.

IF a bullet were to encounter say a blade of grass at 10ft from the muzzle and IF said blade of grass were just enough to deflect the bullet slightly with no other harm done then the bullet would be redirected onto a new path as surely as shunting a train onto another rail..........and the piece of grass would have had the same effect as a gust of wind. There would be no reason for the bullet to try to "regain it's original line". The same is true of ALL dispersion factors, none of them have a homing sense.


The only place where I can see a bullet fighting to regain it's original flightpath would be in the instance of shooting a bullet down onto the surface of a lake at an oblique or very low angle...........the bullet will of course ricochet or be deflected upward and gravity will fight to bring it back into line with it's initial path. I say this only to show that force AND direction are required. Absurd as my example is it does set up a scenario where the required FORCE (gravity) is acting in the proper DIRECTION (in this case down) to bring a bullet "back to it's original path" which is the contention advanced by those who believe in dispersion decreasing with range.


There is no attraction to nor affinity for the mythical "original trajectory or flightpath" in a real word bullet. Even the fact that a bullet corkscrews or spirals or exhibits "epicyclic swerve" has nothing to do with rate of dispersion. The fact that it's spiraling, corkscrewing, dropping, drifting, angling down on its intended target is true but what we're talking about is that 5 bullets traveling through the same air will simply follow slightly different paths or "diverge" from their point of origin.



For me, the easiest way to see divergence is to think of a shotgun blast...............5 bullets trying to find the same target are no different than 6 or 8 buckshot pellets or 350 pcs of birdshot trying to find a target. A shotgun "pattern" is the exact same thing as a "group". Now what kind of "choke" would it take or what sort of magical magnet would cause your pattern to begin to TIGHTEN as range increases? Or even Charles to maintain size as in your example of a bullet being "dispersed" to 1" at 100 and then staying at 1" to 200


ref this quote >>>>>> "What I'm saying is, yes, the amount of dispersion already in the flight will be maintained, but will not increase. So, if the bullet has "dispersed" one inch at 100 yards, it will be 1 inch at 200 yards, not two inches. That would be a reduction in MOA, though not in inches."


If this were true Charles then your shotgun blast could theoretically "disperse" out to a certain point (in your example 1") and then STAY THERE like a tube........you could make a shotgun pattern to any yardage.



In fact, if one were to shoot from outside into a tunnel we could lock the RATE of dispersion such that if the rate upon entering the still air was 1moa or 1" at 100yds then the rate would remain unchanged so that you would maintain 2moa (or 2") @ 200yds and on to 3moa (3") @300 but you could never bring the dispersion back into parallel with the projected hypothetical "center of trajectory". That would be like re-collecting shotgun pellets or making a shotgun pattern stop dispersing and turn into a parallel tube of pellets........This would allow me to hit ducks at 100yds......



Nope, rate of dispersion can never decrease nor even truly stabilize, it can only increase..............groups can only get bigger, not only in inches but in minutes of angle of dispersion.


What I'm saying is that a 1" group @ 100 will never be less than a 2" @ 200, 3" @ 300, 4" @ 400 and so on........



I KNOW that some heavy hitters like Gale McMillan insist that there's magic or "unexplained ballistical phenomena" while I insist that there isn't.

Credence-wise Gale can swamp me :)

Science-wise he ain't got a leg :)



Where some folks get confused is that moa measurements implicitly contain more information than measurements of groups in inches. Minutes of angle simply ARE an expression of rate of divergence while groups as measured in inches are range dependent and the rate of divergence must be inferred or added.



And it's the RATE of divergence that interests us......





al

alinwa
01-05-2008, 05:01 PM
BTW Boyd ;)


The last time this happened (The Mother Of All Wind Drift Threads >>>> http://www.benchrest.com/forums/showthread.php?t=43279&highlight=alinwa+winddrift <<<<< ) we reached an impasse of OUR understanding, or perhaps our ability to communicate our premises, not the end of knowledge. I contended one thing while my 3 or 4 "opponents" contended another............and I declined to continue out of a sense of futility NOT because we were in territory about which there were no answers. I will STILL contend as I did then but only when there are no tempers or egos involved. To a true ballistician we're all just a bunch of squabbling kids trying to grasp simple concepts. BUT, this is no different that us discussing "Quantum Physics" or what was referred to in the old daze as "Rocket Science" ...... YES WE are a little out of depth but we'll learn as we go and hopefully we'll all gain from the discussions. ('cept for those of us who'd rather be somewhere else ;) and to you I politely ask "WHY are you here?")


This is all good stuff and those of us who ARE interested will continue to forage because it's worth it to US.


To all the rest of y'all, go back to your reloading or whatever......ain't nobody forcing you to clik here :)



al

Charles E
01-05-2008, 05:02 PM
Al,

I'm not sure it is woth continuing, but consider this,

Suppose there is a 10 MPH crosswind wind blowing. It is a normal wind, it just keeps on a blowin. The bullet will be off so much at 100, and so much (more) at 200.

Now consider a magical wind. It is jsut like the first one, but magically quits as the bullet passes 100 yards. You aren't saying that the bullet in the this case drifts the same amount at 200 yards as in the first case, are you?

Now consider magical condition 3: The wind blows left to right for the first 100 yards of the bullet's flight. It instantaneously & completely reverses for a little over the next 100 yards of flight (whatever it takes so the drag is equal). Where does that bullet wind up?

While we don't encounter these magical conditions, I think we also don't encounter the steady, constant wind in the first example all that often. The air, near the ground, and over varying terrain can give rise to funny forces acting on a bullet.

Just my attempt to offer a possible explanation why some people feel a rifle can group better at 200 than at 100.

J. Valentine
01-05-2008, 05:05 PM
I think the British were just practising Psychological warefare ! The cunning little devils.

alinwa
01-05-2008, 05:16 PM
Charles,


Magical Condition #1 ----yes

MC #2 ----no, unlike number one where the sideways accelleration is continued to 200yds it will "straighten out" but it will "straighten out" at an angle to its original path. It's path will show a smooth curve for the first 100yds and a straight line thereafter........the straight line though will DIVERGE from the original it will NOT resume parallel flight.

MC#3 ----back on target or back to original LOS if the total drag force/time is reckoned or the equation is balanced. Of course this is a little dicey as you pointed out by saying "for a little over the next 100 yards".... I understand completely what you're conveying.


al

bsl135
01-05-2008, 06:46 PM
Good evening fellas,

I remember this discussion clearly from last winter, it's like deja-vu.

The topic sent me on a quest to discover if the cause of smaller MOA groups at longer range could be caused by epicyclic swerve (corkscrew flight path) thru the use of modern 6-degree of freedom computer simulation. I tackled epicyclic swerve because it's the ONLY external ballistics mechanism that could conceivably be responsible for the observed behavior. One may say that 'magical' wind conditions could blow groups apart at close range and then blow them back together at long range. Granted. But this WILL NOT happen on a repeatable basis.

I posted my analysis on my website (http://bryanlitz.bravehost.com/):

click on 'epicyclic swerve' on the left.

Suffice it to say, my analysis of epicyclic swerve is not in agreement with Chris Long's, mentioned in a previous post.

This thread has a lot of the same claims from the true believers that we've all heard before. Without any new information, I'm sticking to my conclusion that I arrived at at the end of my modeling project: IF the effect happens, it's not caused by anything dealing with external ballistics. I suspect optics (parallax, or other optical conditions). This explains why it always happens for some people and never for others.

Take care,
-Bryan

alinwa
01-05-2008, 06:47 PM
Regarding the other, the fact that folks DO tend to shoot better groups as range increases..... (well, to a point. Anything beyond about 600-700 and Old Ma Nature begins to well and truly MESS with trajectories :) ) ........ anecdotally it's true. But it's not all about inherent accuracy or dispersion. Regarding the contention that "nobody knows" this is simply not true. Tens of thousands of groups HAVE been shot through multiple targets and with mapped trajectories and NEVER has a condition been shown where convergence occurs. ANYONE can set up two targets and many folks have the financial wherewithal to set up an acoustic at 100 and then onward to a target at whatever yardage is desired. Brute force testing is easy, showing WHY things are as they are can be daunting. This is where Harold Vaughn did us a great service with his book, he applied himself to the WHY.


Regarding the fact that bullets DO drift downwind there's little argument, it's the WHY, the actual mechanism that's intriguing.


MOST folks though would rather opine than test. And many folks simply will not take the time to learn enough about a subject to be conversant.




an example;

We had a situation a while back where a friend of mine ran a 2" PVC pipe from a pond down to a building. This man owned a large backhoe and he simply ditched from the pond DOWN to the building, his intent was of course to "suck" or "siphon" or let gravity "pull" or whatever...........he knew that water ran downhill and he figgered that water would "run" thru the pipe to the building. It stands to reason :)


WRONG!!!



The pipe was a mile long and it dropped 700feet.


And it would NOT run water. With a pump at the top "PUSHING" water into the line it would NOT ALLOW WATER TO RUN DOWNHILL!!! You pour water into the top and it doesn't come out the bottom.......It's rather frightening to experience, kinda' like taking a satisfying dump and turning around to see no trace of your action.....


He spent a freakin' YEAR hashing this around before he ran across a trained and experienced hydraulics guy..........he had discussions with all sorts of "experts", even paid money to let "engineers" (folks who'd passed engineering courses in college and were "certified") analyze the situation and suggest fixes. He went thru and dug up the line every hundred feet to find out where it'd broken. TIME was spent.


I was visiting with him maybe half-way through his oddysey and he brought me up to speed, I was intrigued so I asked everyone I knew........NONE of us knew enough nor did we learn enough in that year to make water run downhill, until I was talking with my uncle who'd spent time working on irrigation systems. He explained how to make the line work. He wasn't perfectly clear on the WHY, or at least wasn't able to get the "why" through my thick skull but he knew HOW to make a line take water and he was certainly aware that just running a line would not work.


In the meantime the fellow ran a shorter 1" line from a spring only 50' above another cabin and 200ft away..........this line worked for about 6mo until someone "shut it off wrong" and it quit. You could then re-prime it by taking a generator and a pump up to the top and ramming water down it or by saving a basin of water down at the bottom and pumping it up from the bottom. This was the eventual "fix" for the problem with the short pipe but it did nothing for the long one.


Note that in both cases the lines were plumbed into the springs below the surface and pitched ALL downhill.



What I'm trying to illustrate here is that we weren't stupid, just ignorant. And we were dealing with stuff that we assumed was simple but in fact wasn't. After a year of intensive searching and the hiring of several "expert engineers" there were folks who were saying that we were in "unknown territory"...............and they were very partially right. It WAS unknown territory for US and even for the supposed "experts" but it was certainly old and well traveled territory within the hydraulics industry.



Since then I've met quite a few folks who understand the problem, some who broke into delighted laughter at the thought that someone would be so silly as to try to pipe water downhill! Folks who had both theoretical and the field experience to draw upon.


Until there's a market for truly experienced ballisticians, or until one of the techs down at Aberdeen joins the board we'll have to settle for learning as we go and discussing with people who've been to school for "ballistic engineering". And NO, engineers conversant in fluid dynamics or hydraulics are NOT necessarily equipped to understand bullet flight. And NO the ballisticians down at the bullet companies don't automatically know the answers.........some of the stuff they've come up with in books and on this board have been shown to be poorly researched. Lots of folks can quote chapter and verse from the textbooks but knowing how to apply formulae is far from understanding.


Regarding this sort of discussion, I'm the last person to bash the internet. This resource has done more to disseminate information in a shorter time than even the printing press. It's an awesome resource. I'm really blown away by the Wikipedia concept.......I once bought an expensive set of Encyclopedia Brittanica just because they used a similar approach, I've since given them away because they were eclipsed by the internet. By the same token I've spent endless hours discussing word definition, proper usage and application of the English language, comparison of various dictionaries and textbooks, even messed around with the concept of "historical accuracy". Frustrating stuff! The wiki concept and the internet open up worlds of resource to the researcher.


Physics, unlike language is much more well defined. Mathematical parameters are easier to establish and "prove" than language concepts but even in the mathematical and physical sciences the established way of doing things has been kinda' bass-ackwards thru the years........the course of development has been to empirically establish data sets and then try to reverse-engineer theories to fit the data.


THIS one though is fairly straight forward, until someone can SHOW groups with lessened dispersion as yardage increases then why go to great lengths to prove/disprove the contention? What's to reverse from?

And anecdotal stories don't count.

My favorite is the guys who'll shoot 50BMG tracers and watch the spiraling fire-trail grow "smaller" as it goes away down range until it's just a point of light...........these guys are convinced that the bullet is "going to sleep" and "finding the center of trajectory" when even if it were TRUE it has no bearing on dispersion of groups of rounds fired.


Whewwww...gotta' finish this off and regroup my brain here! I'm getting scattered.


THANK YOU ALL who perservere! And may we all find new and better understanding through discourse :)


al

alinwa
01-05-2008, 06:52 PM
Hi Bryan, I'm a slow typist and you slipped in while I was laboriously composing my thread.....this thread contains no references to yours.


WELCOME!!! :):):):)


I'm glad to see that you're here.


Now I've got to go back and read thru start-to-finish and see how many times we've leapfrogged and inadvertantly counter-pointed in this thread....


al

Don
01-05-2008, 08:45 PM
Good evening fellas,

I remember this discussion clearly from last winter, it's like deja-vu.

The topic sent me on a quest to discover if the cause of smaller MOA groups at longer range could be caused by epicyclic swerve (corkscrew flight path) thru the use of modern 6-degree of freedom computer simulation. I tackled epicyclic swerve because it's the ONLY external ballistics mechanism that could conceivably be responsible for the observed behavior. One may say that 'magical' wind conditions could blow groups apart at close range and then blow them back together at long range. Granted. But this WILL NOT happen on a repeatable basis.

I posted my analysis on my website (http://bryanlitz.bravehost.com/):

click on 'epicyclic swerve' on the left.

Suffice it to say, my analysis of epicyclic swerve is not in agreement with Chris Long's, mentioned in a previous post.

This thread has a lot of the same claims from the true believers that we've all heard before. Without any new information, I'm sticking to my conclusion that I arrived at at the end of my modeling project: IF the effect happens, it's not caused by anything dealing with external ballistics. I suspect optics (parallax, or other optical conditions). This explains why it always happens for some people and never for others.

Take care,
-Bryan

http://www.nennstiel-ruprecht.de/bullfly/fig12.htm

Mike Marcelli
01-05-2008, 10:04 PM
AERODYNAMIC DRAG:
Definition: The drag produced by a moving object as it displaces the air in its path. Aerodynamic drag is a force usually measured in pounds; it increases in proportion to the object's frontal area, its drag coefficient, and the square of its speed.

When certain bullets leave the barrel, they precess, like a top. If you picture the frontal area of a precessing bullet, it is displacing an effective area greater than the true diameter of the bullet. Once the bullet goes to sleep, the frontal area decreases to the true diameter of the bullet and the drag decreases.

In a cross wind, the precessing bullet will "drift" proportionally more than the bullet that has ceased precessing. So, if you have a constant cross wind acting on a bullet from 0 to 200yds, and the bullet does not cease precessing until late in its 100 yd travel or between 100 and 200 yds, it is possible that it will be deflected less than the expected MOA of the 100 yd group.

This doesn't defy any laws of physics because the force on the bullet, i.e., the drag, is changing in an otherwise static condition. I'm not talking about the total angular dispersion that occurs in a wind free environment improving at 200 yds. I'm talking about the dispersion brought about by the cross wind component.

Dave Short
01-05-2008, 11:02 PM
AERODYNAMIC DRAG:
Definition: The drag produced by a moving object as it displaces the air in its path. Aerodynamic drag is a force usually measured in pounds; it increases in proportion to the object's frontal area, its drag coefficient, and the square of its speed.

When certain bullets leave the barrel, they precess, like a top. If you picture the frontal area of a precessing bullet, it is displacing an effective area greater than the true diameter of the bullet. Once the bullet goes to sleep, the frontal area decreases to the true diameter of the bullet and the drag decreases.

In a cross wind, the precessing bullet will "drift" proportionally more than the bullet that has ceased precessing. So, if you have a constant cross wind acting on a bullet from 0 to 200yds, and the bullet does not cease precessing until late in its 100 yd travel or between 100 and 200 yds, it is possible that it will be deflected less than the expected MOA of the 100 yd group.

This doesn't defy any laws of physics because the force on the bullet, i.e., the drag, is changing in an otherwise static condition. I'm not talking about the total angular dispersion that occurs in a wind free environment improving at 200 yds. I'm talking about the dispersion brought about by the cross wind component.


This makes sense and is well stated.

-Dave-:)

RayfromTX
01-05-2008, 11:31 PM
Not really.

bsl135
01-05-2008, 11:45 PM
The link put up by Don is a pretty good illustration of fast and slow arm epicycles. This is how bullets fly when they're launched with an initial yaw angle, or angle rate.

Mike gives a good description of the effect of precession on drag, and the increased wind sensitivity for bullets flying with significant levels of yaw.

The point I wish to take issue with is the assumption that significant yaw is always present. Many people will contend that all or most bullets fly a few hundred yards before 'going to sleep', and that the yaw levels are such during that time that drag is significantly effected. This is not the case. Especially for finely tuned target rifles shooting 1 MOA or less, there cannot be significant levels of initial yaw, or 1 MOA groups would not be possible.

What I mean by 'significant' levels of yaw are yaw levels that have a noticeable effect on drag. In most cases (ie, unless there's something wrong) any fast arm yawing is gone within 15-20 yards. If the projectile is dynamically stable (most are until past 600 yards) the slow arm will also dampen, but it may take a whopping 50 yards. Add to this any yawing motion caused by mass imbalance, and you may be looking at a full 1 or 2 degrees of yaw at any given point in the first 100 yards of flight. This is not enough to affect drag. In cases of borderline static stability, the bullet may exhibit larger angles, but this will cause very large groups, and the above statements about increased wind sensitivity mentioned above would apply. However, when everything's working the way it should, and you're grouping 1 MOA or less, there is not enough yaw to effect drag.

I've also done a write-up on this subject on my website (http://bryanlitz.bravehost.com/) which is based on 6 degree of freedom modeling. Click on 'Ballistic Coefficient Testing' on the left.

For those who don't care to read the details, it boils down to this:
A 25 radian per second initial yaw rate (tip-of rate) is considered very large. It will result in the bullet striking 0.75 MOA from a bullet fired with no initial yaw rate (direction of impact depends on direction of initial angular motion which is random). This bullet starts out at less than 2 degrees of total yaw (angle-of-attack), and dampens to less than 0.4 degrees by 100 yards. The velocity of this bullet at 100 yards is only 0.3 fps less than a bullet fired with no initial yaw rate. The take-away here is that good groups would be impossible with bullets having initial yaw rates anywhere near this. The groups couldn't be smaller than 1.5 MOA. This much dispersion caused by such high yaw rates only effects drag enough to cause a 0.3 fps difference in velocity over 100 yards!
*The example is for a .308 155 grain Sierra Palma bullet, 1:13" twist.

So it's not that we misunderstand yawing. It's not that bullets don't 'go to sleep' and are more sensitive to wind when yawing, etc. We just misunderstand the magnitude of the effects. All I'm saying is that for normal competition rifles shooting 1 MOA or better, there is not enough yawing at any point in the bullets flight to effect drag or wind sensitivity.

Good night all,
-Bryan

GARMASTERS
01-06-2008, 12:40 AM
Once in motion a bullet undergoes a deflection from its intended path. This deflection is called the "Coriolis Effect" and is a result of the earth's rotation.
The practical impact of the Coriolis effect is mostly caused by the horizontal acceleration component produced by horizontal motion. There are other components of the Coriolis effect. Eastward-traveling bullets will be deflected upwards, while westward-traveling bullets will be deflected downwards. This is known as the Eotvos Effect. This aspect of the Coriolis effect is greatest near the equator. In addition, bullets traveling upwards or downwards will be deflected to the west or east respectively. This effect is also the greatest near the equator. Since vertical movement is usually of limited extent and duration, the size of the effect is smaller. The amount of deflection the bullet makes is directly related to both the speed at which it's moving and its latitude. Therefore slower bullets will be deflected a smaller amount, while faster bullets will be deflected more. So there will be more Coriolis Effect at 100 yards and less at 200 yards as velocity decreases.

bsl135
01-06-2008, 01:09 AM
Therefore slower bullets will be deflected a smaller amount, while faster bullets will be deflected more. So there will be more Coriolis Effect at 100 yards and less at 200 yards as velocity decreases.

Please don't take offense, but this is not true at all.

The Coriolis 'effect' is an acceleration. The amount of bullet drift due to Coreolis, or any other acceleration depends on time of flight. The more time something accelerates, the faster it moves and the further it diverges from it's original path. Therefore, faster bullets are deflected less than slower bullets by a constant acceleration.

The Coreolis effect is not even relevant to the current discussion about groups of bullets since it's equal for every shot fired at the same latitude in the same direction.

-Bryan

alinwa
01-06-2008, 01:10 AM
GARMASTERS,

And how does this pseudo-force based solely on frame of reference affect dispersion? And how do the slower bullets show less deflection? I'm honestly confused by your post, It looks like a cite but one I'm not familiar with it so can't check it for frame of reference.

What are you saying?



al

alinwa
01-06-2008, 01:12 AM
BRYAN!!!! YOU DID IT AGAIN!!! :):):):)


I thought you were in BED man!


Again, you posted whilst I wrote, sorry!


al

Lynn
01-06-2008, 01:52 AM
Tell your friend with the water pipe that if he left the path open instead of using the pipe the water would run downhill without any problems.If you ever get to the Tehachapi Mountains in Southern California stop at the Edmonston Pumping Plant for a tour.They pump the water for the aqueduct and the motors are rated at something like 1,100,000 horsepower.
Oh yeah if you shoot a tracer in a 50 bmg that starts out at 647 grains it will lose 300 plus grains during its time of flight.At 1000 yards it flies like any bullet does.At 2200 yards the path is a slow clockwise corkscrew until it lines up with the target then a long straight drop.The path appears the same in the calm as it does in windy conditions even though the point of impact is different.
Lynn

Sonof A. Gunn
01-06-2008, 03:03 PM
Amazing how this silly argument has come up again and especially that NO one has taken the time to do some basic, simple tests* to contribute verifiable results for all to see and maybe hopefully settle this.

No one seems (unless I missed it wading thru all the "bull-istics theorizing") to have mentioned what may very well be the causative factor in the instances where group size has (apparently) improved over longer distances - parallax error. IOW, the optics were adjusted for correct parallax at the longer ranges, but INcorrectly adjusted (parallax error) at the shorter range - very common error especially among novice target shooters.

*All that has to be done is to set up multiple aligned targets at several ranges and fire groups (at least 5 shots; more better) thru them simultaneously so bullets print on all targets. This should be done under no wind conditions (or in a tunnel or warehouse) and could be done with assorted guns/calibers for a variety of results.

Especially interesting would be to use a rail gun which would eliminate any human or parallax error.

Come on, somebody here ought to be able to do this and post results w/group images for all to see. One day or an afternoon is all it should take. Anyone? :confused:

Of course, as one has posted, the NRA and military has done this. How about a link to the info?

BJS6
01-06-2008, 03:30 PM
In terms of the vertical dispersion only, I have certainly heard about a certain combination of load and rifle in the old British SMLE that would show a reduced vertical MOA spread at long range than at short. The theory was that the barrel vibration pattern with that load was such that the slower rounds left the muzzle with the barrel pointing higher than the faster rounds and thus had a self compensating effect for the velocity variation.

I am sure Varmint Al demonstrated the same thing with his 6PPC modelling. It was possible to tune the load to the barrel exit point such that the slower rounds pointed slightly higher on the target and thus compensated for the added drop of the lower velocity.

I know my BR rifle shoots higher with a 28.8 grain load than it does with a 30.0 grain load even though the two group about the same. If I was to shoot a composite group with 5 rounds of each load the group at 100 would be something like a 0.7 with two distinct clusters. If I shot the same 10 rounds at 200 or 300 isn't it possible that the higher point of impact with the slower rounds at 100 yards would compensate for the added drop of the slower rounds at longer range and thus the MOA measure of the overall group would in fact be less ?? Maybe not 200 or 300 but there must be some specific distance where the higher point of impact at 100 yards would offset the added drop and the two groups would converge and make one group smaller in MOA measure than at 100 yards ??? That of course is an extreme case but I'd imagine the same thing is entirley possible with a normal load variation, the barrel vibration and point at bullet exit relating favourably with the velocity variations so that the vertical MOA is less at certain ranges than others.

J. Valentine
01-06-2008, 03:50 PM
Amazing how this silly argument has come up again and especially that NO one has taken the time to do some basic, simple tests* to contribute verifiable results for all to see and maybe hopefully settle this.

No one seems (unless I missed it wading thru all the "bull-istics theorizing") to have mentioned what may very well be the causative factor in the instances where group size has (apparently) improved over longer distances - parallax error. IOW, the optics were adjusted for correct parallax at the longer ranges, but INcorrectly adjusted (parallax error) at the shorter range - very common error especially among novice target shooters.

*All that has to be done is to set up multiple aligned targets at several ranges and fire groups (at least 5 shots; more better) thru them simultaneously so bullets print on all targets. This should be done under no wind conditions (or in a tunnel or warehouse) and could be done with assorted guns/calibers for a variety of results.

Especially interesting would be to use a rail gun which would eliminate any human or parallax error.

Come on, somebody here ought to be able to do this and post results w/group images for all to see. One day or an afternoon is all it should take. Anyone? :confused:

Of course, as one has posted, the NRA and military has done this. How about a link to the info?

Only one problem with that is when this was supposed to have happened they used peep sights not scopes.

J. Valentine
01-06-2008, 03:55 PM
Hi Bryan, I'm a slow typist and you slipped in while I was laboriously composing my thread.....this thread contains no references to yours.


WELCOME!!! :):):):)


I'm glad to see that you're here.


Now I've got to go back and read thru start-to-finish and see how many times we've leapfrogged and inadvertantly counter-pointed in this thread....


al
Alinwa , The best way to grab your spot in the thread is quickly post a few words then reopen in edit and continue writing. That way it will reserve your spot.

Lynn
01-06-2008, 04:31 PM
I believe Henry Childs has done this test many times over acoustic targets like Alinwa described.The groups get larger each time but nobody here seems to believe the results once they are given.
Lynn

Sonof A. Gunn
01-06-2008, 04:55 PM
Quote: "Only one problem with that is when this was supposed to have happened they used peep sights not scopes."


When what happened and who is "they"? Why is it a problem?

alinwa
01-06-2008, 09:27 PM
Lynn,

Thanx for confirming that water in an open ditch will still run downhill :D

Sonofagun,

All of the points you mention have been addressed and documented in past. Bryan posted in this thread about parallax error and has brought it out on past discussions.

Bryce,

You must have a rifle shooting perty good if you can see the sine wave printing on your target.....good on ya!!

J. Valentine,

Thanks for the heads up. Good idea, I hadn't thought of that.


Lynnagain,


YUP, I agree that that's a problem. A whole bunch of folks are so wrapped up in wanting to believe in magic that they refuse to accept tested FACT. :) A quick drive through any old-town will confirm this...........look how many acupuncturists, palm-readers, naturopaths and butt-swabbers are doing booming business between the pawn shops and paycheck loan places.......OOHHhhhh, I'm sorry! "colo-rectal massage and lavage therapists"......no offense to the retentives reading :D:D


Big as life, main street downtown where I live "COLON HYDROTHERAPY and CANDLING, pets welcome!".....UN-believable!


And we wonder why folks want mystery? It's just to distract them from their private reality!!


LOL


al

Sonof A. Gunn
01-09-2008, 04:10 PM
Sonofagun,

All of the points you mention have been addressed and documented in past. Bryan posted in this thread about parallax error and has brought it out on past discussions.


al

OK, so once again this topic is discussed to death without anybody even saying they'll go out and do some shooting to settle this one way or the other to which I say...

WTF!

:confused:

Strong suggestion: Wilbur, close this thread!

Lynn
01-09-2008, 05:20 PM
I think what Alinwa is trying to say is its all been done before and posted here as well.
I had a gun that I thought was shooting smaller at 300 yards than at 100 yards.Henry Childs told me I was daffier than a famous duck.He told me to line up several targets so a bullet hitting the 100 yard would also go through the 200 or 300 yard target whichever distance you think is the best grouping.I pounded some rebar in the ground and wired a 2X4 to it at each distance so a target could be stapled up and the problem went away.
I also used a bullseye at 300 yards to hit a target at 100 yards and vica versa.In that situation I shoot better at 100 yards when I'm aiming at something 300 yards away.
The test is very to do if you have a portable bench.I was trying to do it at our local range and the 100 200 300 yard berms have too much elevation to make it work.You need a flatspot.
Henry has actually done this test across a pair of Oehler 43's not the much cheaper Oehler 35's and used acoustical targets as Alinwa recommended.That is exactly why he knew what I would see.
Wilbur shouldn't pull a thread unless it's somebody picking on a gunsmith.
Lynn
P.S. Now that I think about it check the 1000 yard forum.I don't think Henry would post on this one and that is probaly why it is familiar to Alinwa as he hits them all.

BJS6
01-09-2008, 05:32 PM
Lynn,

I am not saying I disagree because I just don't know if my idea has any basis in reality, just wanting your input.

Varmint Al posted in his 6PPC barrel vibration modelling posts that you can tune the load so that the bullet exits just before or after a high or low point in the barrels vibration. Done right the slower bullets will exit when the barrel is pointing higher to offset the velocity variation.

Now I can observe a change in point of impact at 100 matres with different loads in my 6PPC. A load at 28.8 grains impacts notably higher than at 30.0 grains. If I shot loads with a wide variation of velocity, even intentionally loaded with variation in powder weights, isn't it possible that a slow load would hit high at 100 but out at some longer distance the higher barrel point along with lower velocity will result in less vertical in MOA terms at that longer distance than the same rounds would shoot at 100 metres ???

Seems perfectly logical but maybe I am missing something here.

Bryce

Lynn
01-09-2008, 05:54 PM
I shoot 600 and 1000 yards and use some big cases from time to time.In doing my load work-up I may start at 73 grains of powder and go past 83 grains of powder.If you go up incrementaly in say 0.5 grain jumps your target will show vertical then a flat spot that rolls off just a touch right before the shots start to climb again or go vertical.I always find my best accuracy at that point.

Occasionaly you will ge a shot that is way low for its powder charge.If a guy was to think the bullets converge farther out that is the charge I would use in my testing.

In my case I didn't think the groups were opening up in the correct MOA proportional to the distance shot.

In your example it sounds like your looking for a down range convergence using two different loads? Were one hits high and the other hits low and at some point they will meet or converge.Interestingly enough Australia's Jeff Rogers(aJR) thinks along those same lines and also posts on the 1000 yard forum.

I also was under the impression Alinwa himself thought convergence was valid?
Lynn

BJS6
01-09-2008, 06:45 PM
Two different loads ?

Here is my scenario. At 100 metres 28.8 grains N133 and a Barts Ultra will impact something like 0.7 inches higher than the same load with 30.0 grains N133. So if I had a poor loading system and had a ten shot group with 5 each at 28.8 and 30.0 I'd have a 10 shot group with bout 0.7 of vertical and two seperate groups.

Lets assume that at 300 metres the extra elevation of the slower load compemsated for the lower velocity and increased drop. It has to be that at some stage those two set of 5 rounds would converge, it may not be 300 but at some distance they simply have to, they can't possibly not cross trajectories, can they ???

So lets assume it is at 300 metres that they cross. Both loads will shoot sub 0.20 at 100 metres but as a composite group (like might happen if the ammo was loaded poorly say) would have about 0.7 MOA vertical. At 300 metres if the trajectories converge the 10 shots are not likely to have 0.7MOA in good conditions. Logically the 10 shots at 300 would have a lower MOA spread than at 100.

Now if the loads were spread over a range of powder weights from 28.8 to 30.0 grains wouldn't the same hold true ? Each shot would have a different velocity and a different trajectory but each faster one would start off with effectively a lower elevation at 100 and less drop by that assumed 300 metres distance. The result being the same vertical spread just over a range rather than two seperate groups at 100 and still a converging of trajectories at that assumed 300 metres.

Why could the same not hold true for normal loads with some velocity spread greater than ideal that happen to coincide with the point just before or after a trough or peak in the barrel vibration depending on the velocity ??? Logically you could create a situation where you had more spread close in than out at range or more spread out at range than close in. All that you'd be doing is tuning the load to be ideal for the distance you are shooting at or for a different distance.

Will the best 1000 yard load for a 6.5-284 say always be the same as the best 100 yard load or 300 yard load ?? Couldn't some added vertical at say 300 yards actually help at 1000 yards if the higher shots were the slower shots ???

What am I missing ??? Why is that not entirely possible ???

Bryce

Lynn
01-09-2008, 06:59 PM
Bryce I think we are thinking the same thing on your first point.I consider 28.8 and 30.0 to be 2 different loads.
In that example like you I think they have to cross paths somewhere.
On the second part were you are staring at 28.8 and going up slowly to 30.0 I don't see what you are seeing.In my guns as you go up in powder charge you see vertical except for that one freak load which in your case would be 30.0 grains of N133 hitting lower on the target.
I have never shot that freak load as I call it.In my guns going up 0.1 grains after that freak load always goes back to being vertical with a higher impact point.
Lynn

BJS6
01-09-2008, 07:09 PM
Lynn,

In my situation, based on a few 5 shot groups while fine tuning, as the powder weight increased the point of impact walked down the page. As I hit 29.8 grains the group was as low as it would get and at 30.0 and 30.2 grains the point of impact started to climb again. All these groups were much lower than the previous accuracy node at 28.8 grains.

It seems that if I fired groups at 0.2 grain steps from 28 to 30 plus grains on targets right beside each other I'd end up with a nice curve plotted out based on the centre of each group.

As I understand it that is the same as "Rifle accuracy facts" demonstrates with varying loads shot in a rail gun. The point of barrel exit of varying loads will alter the point of impact depending on the vibration and velocity.

While my point is purely theortical I can see that if I intentionally or otherwise loaded ammo over a small range of weights either side of 29.5 grains I could get less spread at some longer distance than at short range, in MOA terms at least.

Perhaps short stiff PPC barrels twang about differently to longer heavier barrels on 1000 yards rifles ???

Bryce

bsl135
01-09-2008, 07:14 PM
Bryce,
The situation you describe is perfectly logical. In fact, the effect you describe is the basis for 'ladder testing' that you occasionally read about. So many people say that you must test your loads at the intended range to truly know how it will perform there.
I proposed this as a possible explanation for the non-proportional grouping when this conversation came up last year. I was told by most of the shooters who have observed the effect that the groups (big and small) were round. This kind of negates velocity and barrel vibration as the culprit. If velocity variations and barrel vibrations were to blame, the close groups would be all vertical. That's not what's observed by those who report this behavior.
The more this topic is discussed, the more I'm convinced that optics are the culprit. Lynn's experience certainly suggests optics. If nothing else, we can all have a valuable 'take away' from this discussion: check your parallax! You may actually have a world class rifle & load, but suffer loss of precision from parallax. Such a problem would be hard to discover unless you specifically look for it.

Son-of-a-gun,
You seem to be pretty upset about the lack of action on this problem. In fact, many folks have done work and posted their results. Personally, I spent 2 solid weeks of computer modeling to find out if epicyclic swerve (corkscrew flight path) was the culprit. I showed thru computer simulation (the only practical way to study epicyclic swerve) that it was not. Lynn, Donovan, Bryce and others have also shared their observations and efforts.
What contributions have you made to this study?

-Bryan

BJS6
01-09-2008, 07:41 PM
Thanks for the extra info Bryan.

I do believe the vertical spread thing is a valid way that a group at shorter range could in fact be bigger MOA than at longer range, it could happen in certain situations.

You say that the observation was rounded groups which rules out what I was talking about as a possible solution, unless some wind was at work and added some horizontal to the vertical and made round !! :)

Bryce

Lynn
01-09-2008, 08:34 PM
Bryce I have never seen a bunch of shots hit lower on the paper as you describe with a rifle.I have heard of this being true with a pistol.
In a pistol a slower shot takes longer to exit the barrel so you end up getting more vertical out of it.Atleast that is the story I heard.
The closest thing I have to a shortrange gun is a 6BR with a 21-3/4 barrel 1.450 straight cylinder.It climbs as the powder charge climbs.
In Vaughn's book the roll-off he is talking about is very small I thought.
Typicaly when I do a "Audette" 'Ladder" or whatever anyone calls it I take it out to 300 or 400 yards.At 100 yards you get a big hole after 10 to 15 shots and it ruins your test.At 400 yards your shots seperate for 4 or 5 shots then they do what looks like a slow shift to the right.As you go up in charge weight the very next shot that goes vertical moves back into alignment with the other vertical shots.So picture this 5 shots going up in a straight line then 4 shots going to the right for about 1 inch.The very next shot goes right back into alignment with the first 5 just higher.
That 6th shot moved the most of any shot.
Now as we keep going up it repeats but when they start shifting slightly to the right the number of shots in it are fewer in number.The plateau is narrower.
Now as we continue to go up the spacing between the shots gets larger as we pressure out.
In that example we never had one shot hit significantly lower.If we had gone up in smaller increments like 0.1 grain instead of 0.4 gr at a time is when you get that one weird hit sometimes 2.
If this were a typical 1000 yard heavygun like a 300 Ackley that plateau would be 2.5 grains wide while the second plateau may only be 2 grains wide.It is in the plateau that you see a very small amount of roll-off.This is what I see when I read Vaughn's thoughts in his book.

Our heavyguns will weigh 75 pounds or more and have a 2 inch barrel on them 32 inches long.The stock is solid aluminum and will weigh 40 pounds empty.The barrel block is integral to the stock so there is no chance of it coming loose.The 8-9 inches of barrel inside of the block are bedded in J-B Weld for a perfect fit.The rest system is as close to a machine rest as the rules will allow and I put 75 pounds of lead shot on it as well.It is a pretty stout set-up.

When I see a shot rolling off we are talking about less than a quarter inch at 400 yards.
Lynn

BJS6
01-09-2008, 08:50 PM
Interesting stuff Lynn.

Perhaps my bit of testing was influenced by some other factor and showed me something that wasn't really there, maybe ??

I will test the change in vertical point of impact some more when I get a chance and see what was happening.

Bryce

alinwa
01-09-2008, 09:49 PM
Bryce,


What you're seeing is the basis of "tuning" as it pertains to 100-200yd BR, it is not an isolated case. The "Sine Wave Tuning Method" referenced by Harold Vaughn is the result of years of testing and experimentation on the part of many BR shooters including Jack Jackson and Jim Borden. Jim gives seminars (or at least used to) wherein he describes the tuning method which includes double-blinding your loads and then shooting across a grid for vertical at 100 or 200 yds. While using this method it is expected that your group centers will walk UP and DOWN as you go up in powder charge.

It takes very accurate equipment to see this.


A search for "tuning" or "sine wave tuning" might turn up something but the last good rundown that I remember was lost when we changed to the "new board".


I've got one of Jim Borden's talks on a tape from the '99 IBS Benchrest School, maybe Jim will come on and write a synopsis of how to tune. :) ????


THAT would be one for the FAQ's.............


al

HovisKM
01-09-2008, 10:24 PM
Put a "T" in the pipe up toward the top so that it will VENT. Simple. I learned that when I was four, just don't ask how, still gives my dad an anxiety attack.

Hovis

alinwa
01-10-2008, 01:59 AM
Hovis,

I'm guessing that you're referring to the waterpipe story? Or is this post about Magna-Porting? :D


Yeahhh, as I recall the fix involved putting vents such that each vent pipe came up to just over the base of the previous vent pipe........I THINK that if you just use short vent pipes the water bleeds out up at the top when you shut it off at the bottom. I actually disremember the details except that when they fired that mother up it popped and snorted back and forth up and down the hill like a hiccuping calliope.


It's amazing the difference betwixt theory and reality sometimes. ;)


al