G
GARMASTERS
Guest
Time
In all the time we've spent reading all this think of how much ammo we could have reloaded!
In all the time we've spent reading all this think of how much ammo we could have reloaded!
G
Gerry
Guest
seeking wisdom
Humm i guess you just don't get it Stability. aka bullet wobble.
The pointy bullet didn't settle in till 200 simple'
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.
G
Gerry
Guest
seeking wisdom.
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.
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
Active member
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.
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.
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.
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.
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
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
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
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
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.
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
J. Valentine
Guest
I think the British were just practising Psychological warefare ! The cunning little devils.
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
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
B
bsl135
Guest
Deja-Vu
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:
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
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:
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
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
) ........ 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
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
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
M
Mike Marcelli
Guest
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.
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.
D
Dave Short
Guest
R
RayfromTX
Guest
Not really.
B
bsl135
Guest
Precession: the rest of the story...
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 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
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 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
G
GARMASTERS
Guest
Coriolis Effect
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.
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.