Do Groups Grow Bigger with Distance?

LOL.
I still like "How Bullets Fly"

As I recall (and several peoples reports of vapor trails seemed to confirm) bullets do "corkscrew" in flight and "orbit" the flight path.

Alinwa? Are you getting back to "Wind doesn't push, Drag sucks" again?
 
Vibe said:
LOL.
I still like "How Bullets Fly"

As I recall (and several peoples reports of vapor trails seemed to confirm) bullets do "corkscrew" in flight and "orbit" the flight path.
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This can be viewed quite often in rimfire but I doubt if the bullet is flying along that path of what you see the vapor trail displaying. What I think you see is the vapor trail being moved around by the vortex of the muzzle blast. Have you ever been in the front seat of an airplane following a "heavy" on final approach? I have, and the wingtips that generate those contrails sure don't follow the path you see the vortices taking.
 
Wilbur said:
Have any of Y'all witnessed a case where it SEEMED that groups were smaller (or relatively smaller) at a longer distance - from the same rifle.
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Not seemed.Were.
I'll give you the latest example I have. Three weeks ago, I was working on an old, burned out 300 win mag that was way past it's prime. Severe fire-cracking 5" down from the throat. You know the type, the kind that takes days to get completely clean. Well, this gun wouldn't shoot ANYTHING under 1.5" at 100 yards no matter what powder or charge weight I used. But the bullet that seemed to work best was a 200 grain Accubond. After 6 days at the range, I found a load that shot about 1.5" to 1.75" pretty consistently and had good deviations. I loaded up five more rounds right there on the spot and fired them 5 minutes later at 550 yards. The group went a bit under 4", but four of the five shots were smaller than that with two even touching.
Now I've heard all the theories and excuses (mirage, wind blew it in, parallax, etc etc etc) why this happened, but this has happened so many times I'm actually shocked that more "experts" here haven't seen it too. But, I guess, unless you're shooting long distances with different guns 3 or 4 days a week like I do, maybe you won't see it. But I swear on a stack of Bibles that it happens. And I'd be a fool to witness this as many times as I have and then disregard my own experiences in favor of some "accepted facts" on the internet.
So take it for what you will and do with it as you please. All I'm saying is don't throw away that old gun just because it won't shoot as good as you'd like at 100 yards.;):)
 
Incomplete understanding

As a physicists ( who worked mostly in the optical engineering industry ) I have a reasonably good understanding of the math in books written by Vaughn, Litz etc and have read some of them several times. In several instances I would question the test methods used and the interpretation of that data obtained. Be that as it may. Determining the path a projectile will take during flight is a bit like trying to determine the path a pebble will take during an avalanche. Our knoweldge and understanding of the laws of physics and the language we use to express those laws being mathematics simply isn't good enough to make these predictions with any degree of certainty. Until our understanding becomes better all we can do is make educated guesses.
Andy.
 
Andy Cross said:
As a physicists ( who worked mostly in the optical engineering industry ) I have a reasonably good understanding of the math in books written by Vaughn, Litz etc and have read some of them several times. In several instances I would question the test methods used and the interpretation of that data obtained. Be that as it may. Determining the path a projectile will take during flight is a bit like trying to determine the path a pebble will take during an avalanche. Our knoweldge and understanding of the laws of physics and the language we use to express those laws being mathematics simply isn't good enough to make these predictions with any degree of certainty. Until our understanding becomes better all we can do is make educated guesses.
Andy.
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+1

One of the tenants of science -- even the very general evidentiary system called empiricism, is you can state the conditions under which something that seems true can be disproven. It's not that simple of course, there is a lot of coherence (it fits, therefor it's true) in science, and a good thing.

On the other hand, when you can't state the conditions under which something thought to be true turns out not to be true -- when nothing can count against a belief -- it is like a religious belief. The truth has been revealed, that's it.

Let's keep the two separate, please.

And that is why I like the target test. It is simple, and repeatable. If paper is an area of concern (not sure there is a good basis for this concern, but not sure it isn't, either), we could now use electronic targets.

OK, for the guys saying "in terms of MOA, groups can shrink with distance," what test would count toward disproving this? If there isn't one, there's not much point in talking.
 
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I'm glad someone figured out going through all the targets would do something! My rifles shoots great at 1000 yads but sucks at 600 yards, thought I was going to be able to smash the 600 yard record with my wsm but no go, what shoots at 1000 doesn't mean it will shoot nice tight one at 600. I think your better off tuning for one yardage. So what you trying to figure is its going to change somewhere along the line for better or worse.

Joe Salt
 
Joe Salt said:
I think your better off tuning for one yardage. So what you trying to figure is its going to change somewhere along the line for better or worse.

Joe Salt
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That's true, Joe. Tuning the vertical out for one distance won't work as well for others. Now if you could just learn to reload better, so there wasn't such a spread in your velocities... ;)

Edit:
On a serious note, the test with multiple targets plotted vertical separate from horizontal. If the horizontal is constant MOA, and if the variance in vertical could be explained by velocity difference, The Army & NRA anyway, took the matter as settled.
 
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Can conditions be stated

Charles E said:
+1

One of the tenants of science -- even the very general evidentiary system called empiricism, is you can state the conditions under which something that seems true can be disproven. It's not that simple of course, there is a lot of coherence (it fits, therefor it's true) in science, and a good thing.

On the other hand, when you can't state the conditions under which something thought to be true turns out not to be true -- when nothing can count against a belief -- it is like a religious belief. The truth has been revealed, that's it.

Let's keep the two separate, please.

And that is why I like the target test. It is simple, and repeatable. If paper is an area of concern (not sure there is a good basis for this concern, but not sure it isn't, either), we could now use electronic targets.

OK, for the guys saying "in terms of MOA, groups can shrink with distance," what test would count toward disproving this? If there isn't one, there's not much point in talking.
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One of the major issues scientists face when stating conditions is that no condition is repeatable. No two wind conditions have ever repeated themselves, no two projectiles have ever been manufacturered the same etc. In fact carrying out a test which is also non repeatable in itself fudges the data. It's a bit like things behaved differently because looking at it caused it to behave differently. So where are essentially limited to making those educated guesses. Which for the most part suffice.
Andy.
 
Charles my Spread is 5 fps for ten shots, I finished second for score this year in HG. Just keep getting beat up by the wind. I'm a score shooter Charles, those tight groups out of the scoreing don't do a thing for me. And you and the Army and the NRA are someday going to find out a 0 spread in velocity your still going to get vertical if everything else isn't right. See Charles I've been doing this longer than even you. And what do you mean tuning out the vertical for one distance won't work well for others? Just like everything else find the happy medium nothing is perfect, to many variables. Just be happy when you win!

Joe Salt
 
Joe,

As to tune for different distances, from Varmint Al:

LONG RANGE TUNE.... Here is an interesting set of trajectory plots. No matter how carefully one loads his ammo, there are going to be small differences in muzzle velocity. Consider a load with an average muzzle velocity of 2915 fps with a muzzle velocity variation of 15 fps. Then consider this load tuned for zero vertical at 100 yards that overcomes that small difference in muzzle velocity.

This same load will be out of tune by 73.23-71.50=1.73 inches of vertical at 600 yards. However if the load is tuned so that there is 12.21-11.92=0.29 inches of vertical at 100 yards (with the slower muzzle velocity hitting higher) then there would be zero vertical at 600 yards. This chart is for a 6.5mm 140 gr VLD bullet with a 0.64 BC. A similar chart or table can be made for each long range load. If you are in tune for zero vertical at 100 yards, you will not be in tune for zero vertical at 600 or 1000 yards.
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Or, more important for us, if you tune for 1,000, you won't be in tune at 600. The site is here:

http://www.varmintal.com/aeste.htm

scroll way down to almost the bottom. There is a chart, & like always, a visual makes things easier to see.

* * *

the point about horizontal is, if coning motion changes group size over distance, it will show up in the horizontal spread. Coning is a non-discriminatory phenomena, all planes are equal. But it doesn't show up in the horizontal plots, Q.E.D.

* * *

BTW, I'm score shooter too. Maybe not as good as you, but I always go for score first.

Sometimes that gets me -- like the 2006 Nats at Hawks Ridge. If you remember day 1, you shot next to me in LG, & the wind really came up on our relay, right as we went from sighter to record. I was holding all over the place to try & get a decent score in that gusty 25 MPH wind. Result: big group & low score. You did rather better, don't know what your strategy was. The next day I gave up on trying to center 'em up & shot a group in the 4s I think, with a lousy score. With the 10-inch group from day 1, it was too late for anything but a barely-top-20 in group. You can shoot for group in that crap, but if you can get decent scores, my hat's off to you.

Still, I almost always shoot for score. For one thing, there is one less person to beat (the guy who wins group). Now maybe you're a purist, I gotta take all the help I can get.
 
I'm fairly quick to throw the BS flag when folks are talking contrary to my personal understanding of physics. Jumping the fence on this one and siding with goodgrouper and I think Joe. Would have taken the stand earlier but didn't want to be all alone in the matter.

Not certain that the aforementioned "coning" effect actually exist but, if not, somebody was smart enough to come up with it to explain those occurrences that we have all seen and perhaps experienced.

A quick (I'll try) and perhaps boring story/parable. In 1979, I went through the Westinghouse "Nuclear Theory for Reactor Operators" program. The entire book was handed to us in a loose leaf notebook and was about a hundred pages. After a few days, I decided to get a jump on my classmates and went to the library to check out some related material. I found a bunch of books, mostly written in mathematical greek, but one very thick book actually contained real words. I took it home and read all I could stand only to find out that while the stuff in the Westinghouse handout wasn't even close to what really happened (the details) in a reactor, the "results" were the same. Said differently, an understanding of either would yield the same operator. The "fallout" (pun) of the Three Mile Island" event hit and training changed drastically but I think they're still using that material to explain how a reactor works.

As a sidebar...The operators at Three Mile Island prolly had that nuclear stuff down pat but had an extremely poor understanding of the characteristics of boiling water. Had they simply gone home and left the control room abandonded it wouldn't have been so bad - maybe even a minor incident.

Perhaps the real question is what can we do about our groups if they do not fall into either theory/camp/opinion or disobey physics? That question puts us back to square one for sure.
 
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Wilbur said:
...... The "fallout" (pun) of the Three Mile Island" event hit and training changed drastically but I think they're still using that material to explain how a reactor works.

As a sidebar...The operators at Three Mile Island prolly had that nuclear stuff down pat but had an extremely poor understanding of the characteristics of boiling water. Had they simply gone home and left the control room abandoned it wouldn't have been so bad - maybe even a minor incident.

Perhaps the real question is what can we do about our groups if they do not fall into either theory/camp/opinion or disobey physics? That question puts us back to square one for sure.
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As an aside to Wilbur's TMI story and how what is printed relates to truth sometimes, in the Congressional hearings that took place in the aftermath of TMI, the testifying engineers for that hearing found that the radiation count in that Congressional building was higher than the radiation count in the control room at TMI after the "event".

And Varmint Al and Esten Speers are still learning valuable info about what a barrel tuner can do.....if it weighs enough to do anything worthwhile!!
 
Wilbur I think I like to see what happens for myself before I believe it. I can't put things down on paper that everyone is going to understand, but if I took you by the hand and showed you. Then it would be a little more clear. I helped a guy out this last match in LG. that hasn't gotten all ten shots on paper this year, I think 5 matches. He thought he had a scope problem, but believe me it was more than that. Well needless to say he got all ten on in 18 inches with an 82 score using factory 150 grain 300 wsm Win. amo in the wind! I believe the man is a good writter, but needs a little more of Dr. Joe's common sense. So my thoughts are if your shooting different distances you need to have amo tuned for each one if your going to competitive. And Charles some day I'll explain how I got centered up at Hawk Ridge that week end!

Joe Salt
 
Its OK Wilbur. My personal feeling is your physics BS detection meter needs adjustment. Can't prove it, but here's why.

It's obvious that smaller groups are fired at, say, 200 yards than 100. Just look at the records for 200 yards, and any of my 100 yard targets. And we have a lot of ways to explain that. Wind, shooting skill, reloading skill, rifle build skill, components, on & on.

Now occasionally --I'd bet you've owned a couple, hence your curiosity -- there are rifle systems than, that also occasionally, seem to shoot smaller at 200 than 100. If that "occasional" becomes "always" (or it's cousin, "statistically significant"), we need an explanation other than the usual suspects.

Problem is, it isn't always, just often enough to raise curiosity. Or some people's curiosity. Far as I'm concerned, we still haven't demonstrated a need for any further explanation.

Find one of those rifle/ammo combinations. If we're just talking about 100-200 yard point-blank bench guns, it would be dead easy to set up overlapping targets in the "depth plane" (100 and 200 yards.) Fire groups that print on both targets. I suppose you'd better bring along the chronograph, just as a check on velocity variations.

If, in spite of the curiosity raised about that rifle/ammo combination's capabilities, the groups are the same in MOA, you've got at least one point of negative data. Getting more depends on how curious you are. You aren't ever going to prove a negative.

On the other hand, if the two targets show a smaller group at 200, you've got something that needs to be explained. And you've ruled out a lot of the usual suspects, only one left is wind. And if you can show the phenomena a statistically significant number of times, you can rule out wind conditions, too.

Find a couple more rifles that do this, and the doubters like me are going to start switching sides.

But that's just for jumping up & down & asking for an answer. The answer still matters. What do they say now? The "bullet goes to sleep." What's that mean? Far as I can tell, it's about the same as saying "God wants it that way."

Well, "sleep" is redneck shorthand for "epicyclic pitch and yaw." (I think. I live in that nether region, accepted by neither rednecks or physicists. A lonely place).

Fine, now we've got numbers to use with "sleep." Problem is, I don't believe anyone's ever hooked them up in a predictive model. And if the model can't predict, it's no more use that saying "God wants it that way."
 
Charles - can't say that I disagree with anything you wrote there but calibrating my BS meter would be life changing. That may be a cause of insanity. Imagine waking up one morning with a totally different BS level....

BTW - the smaller group at greater distance thing won't work if you shoot through two targets. Thought everybody knew that! As you said earlier - the Army proved it:)
 
Wilbur said:
BTW - the smaller group at greater distance thing won't work if you shoot through two targets. Thought everybody knew that! As you said earlier - the Army proved it:)
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Besides making it hard to see the farther target. :D
But paperless acoustic targets have been used for such, I think.
As for Going to Sleep - I would suspect that if you shot over a great number of chronographs along the flight path, you'd be able to tell a change in BC when the bullet "went to sleep". I was thinking that they did that at Aberdeen with radar tracking each shot - and measured the coning effect with it as well.
 
The Army proved it Wilbur and numbers don't lie right Charles! And I believe when a bullet goes to sleep that it means it is stable and goes through the wind better like a football or an arrow, it staightens out in layman turms. Don't try and complicate thing more than they already are. And there is no BS. in what I'm saying. So does a bullet that is stable at close range shoot better at long distance, Maybe! If it starts out with the wind not effecting it as much, but is the velocity right for long distance. Like I said nothing is perfect find what works for you.


Joe Salt
 
Joe, that's a great answer. The only problem I've had in this whole thread is with people who try to give an explanation that doesn't fit the facts. Like I said somewhere else -- if chanting a mantra over the rifle worked, I'd chant. Being me, I'd also try to figure out why, but I'd not stop chanting along the way.
 
Interesting Thread

Lots of good discussion here by some very knowlegeable people. :)

The more I learn about this stuff the more I realize just how much I didn't know twenty-five years ago when I thought I knew it all. :rolleyes: My knowledge of riflery and exterior ballistics is far better today but I still have a lot to learn. :confused: It's a fascinating study; isn't it? :D And I've learned a lot right here on Benchrest Central.

Guys, thanks for sharing your knowledge with us, and thank you Wilbur for providing this wonderful forum where we accuracy nuts can have our discussions. :)

I'll sit down now and listen carefully to those who express themselves so much better but in closing let me say this, "Here are three things of which I am absolutely certain."

(1) No one in the world knows it all about anything.

(2) We can all learn something from everyone if we keep an open mind.

(3) A crosswind does not 'blow-on-the-side' of either a bullet or aircraft in flight. :cool:


Best regards

The redneck from West Texas

Gene Beggs
 
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