Applied Ballistics Shoot Thru Target Challenge

[Bryan Litz Ballistics]

Hi guys,

To mark the occasion of Applied Ballistics becoming a proud sponsor of the Accurate Shooter forum, I'd like to pose the following challenge.

First, some background:
There's a common discussion topic based on the observation that some rifles seem to shoot smaller angular groups at longer ranges, for example, 1 inch groups at 100 yards, and also 1 inch groups at 200 yards. This could also be expressed as 1 MOA at 100, and 1/2 MOA at 200. I'll refer to this as non-liner dispersion, which is anytime a rifle groups smaller MOA at farther range.

I've read many discussions about it over the years. I've done a great deal of 6-DOF modeling in attempts to understand bullet dispersion, and have come up short on a ballistic explanation for this phenomena.

Here's my current working theory for explaining the reports of non-linear dispersion:

The first conclusion many shooters come to is that the bullets are actually flying in a way that keeps them from dispersing proportionally downrange. Most discussions about stability, yawing, epicyclic swerve, etc stem from this line of thought. So far I've been unable to identify any aero-ballistic mechanism for this to be possible.
Furthermore on this theory; Lets assume for a moment that the bullet really is flying a corkscrew flight path of constant, or diminishing magnitude. In order for the groups to be angularly bigger at shorter range would *require* that the bullets always passed thru the 100 yard target on the OUTER edge of their orbit, and pass thru the longer range target on the INNER edge of their orbit. We're already out on a limb by assuming that epicyclic swerve is happening (modeling suggests that this only happens on a very small scale, like 0.030") but now we have to also require that there's some pattern to how the bullet passes thru short range vs. long range targets. To me this concept feels like it's way out on a limb, over thin ice.

Now let's take another view.

If you think about how these observations come about, which is someone shooting groups at 100, THEN at 200, a different explanation is possible. This line of thought suggests that the rifle shoots bigger at short range due to some aiming error that's present at short range which is corrected at long range. Parallax is an optical mechanism which can certainly explain this. Another is the size of the target in relation to the reticle being more favorable for 'aiming small' at longer ranges. Finally there's the physiological aspect where shooters may be 'trying harder' to shoot groups at longer range.
The key aspect of this second line of thought is that it allows for these observations (of non-linear dispersion) to be valid, but don't require the bullet to fly a corkscrew flight path.

In order to know which of the above explanations is the true cause of the observed non-linear dispersion, a 'shoot thru' target was constructed at the Applied Ballistics Lab.

You can see the shoot thru target here:

Basically there's a thin sheet of paper held above the line of sight to the 300 yard target. Groups fired at the 100 yard target 'pass thru' and print on the 300 yard paper. By screening the SAME group at both ranges, we can see exactly how the shot group actually disperses. We can aim at the 100 yard paper and shoot a group, then aim at the 300 yard paper and shoot a group, and see how they compare at both ranges. In this way, we hope to discover IF non-linear dispersion actually happens, or if it's just a perception caused by some kind of aiming error. Here's a picture showing the 100 and 300 yard targets with groups printed on both:

Interesting note; the top midle, and top right aim points were shot with a TRG-42, 338 Lapua Mag 1:10" twist and 300 grain Cutting Edge bullets. This was a deliberate test of a low stability case. Note that even though the bullets were key-holing at 300 yards, the groups weren't all that bad and were still proportional to their group at 100 yards. Why the bullets were stable enough to print round holes at 100 and not at 300 is another mystery. To be sure it wasn't interference from the paper, I also shot this same load direct to 300, and got the same keyholes.

Nevertheless; to date we've fired dozens of combinations of calibers, bullets, twist rates, etc. So far NOTHING has shown anything but near perfect linear dispersion.

So where does this leave us?
We have a logical dilemma: "we haven't observed non-linear dispersion in any of the testing that we've done, but we still can't claim with certainty that it doesn't happen because we haven't tested every possible rifle and combination". There are still many shooters swearing they see it on a regular basis.

It's disappointing that we haven't reached a more decisive conclusion, but I'm not giving up yet. So what's the next step? Well, certainly it must be something dramatic, and involve live fire! So here it is.

The Applied Ballistics 'Shoot Thru Target' Challange
I'm inviting any shooter who has a rifle which exhibits non-linear dispersion to the Applied Ballistics Laboratory in Michigan to demonstrate the effect. I'll pay your travel and hotel stay (If you successfully demonstrate the effect, I'll even pay your *return* travel as well ) The objective is to produce a repeatable example of this phenomena so it can be studied and hopefully we can learn what's going on, and if it's how bullets really fly, or not.

This is a friendly challenge with the objective of learning. As much fun as it is to discuss all the theories online, I'd really like to actually solve this one.

Please remember, the objective here is not to speculate about 'how' group convergence happens. Rather, the idea is to demonstrate conclusively on the shoot thru target IF group convergence actually happens or not. If it's discovered to happen, then we can discuss 'how'. Think of this thread as a place to plan and share results of live fire testing on shoot thru targets, possibly in Michigan at the AB Lab.

Of course the importance of this goal goes beyond satisfying curiosity. Currently, it's considered 'common knowledge' by many expert shooters that if a rifle shoots 1.5" at 100 yards; don't worry, it may hold 1.5" to 300 because it's accepted that's how bullets fly. If it's not the case, we can discover why so many people see this, and actually strike at the true cause.

Any takers?

-Bryan

 

[spclark]

Brian it sure is a comfort knowing you're on our side!

Your contributions to practical knowledge about what the heck happens to bullets once they've left the muzzle has certainly improved our lot since you began your career.

Glad to count you as a friend too. I look forward to the next time we get to shoot together. If I had any suspicion any of MY hardware shoots tighter at 300 (or 600 or 1,000 yards) than 100 I'd be taking you on with this challenge!

 

[LRCampos]

.

Nice! I really liked the idea and the "lets put it on the range" aproach.

But I think that this experiment could improve, as there are a couple of things that seems to cause some "noise" on any conclusion:

1- The rifle/load used does not look like an accurate enough. We hope for at least 0,5MOA groups at 100 yards (less is very desireable). The rifle/load used does not look like it get even 1 MOA average. But I can be wrong... and it is not unusual.


2- May be the "long distance" used, 300 yards, is not representative of even the Mid Range used on matches (F-Class Mid Range starts at 300 yards and goes to 600 yards). So, you may not have distance enough, at 300 yards, to get anything more conclusive. I understand that using a far away target may cause anothers variables and practical problems in its own, but...


I am not advocate of any side. I have not enough knowledge or shooting experience in long range to have an informed opinion if the 1MOA-100/300 yards can turn regularly on 0,5 MOA at 300/1000 yards (respectively).

I will love to see the development of this challenge! Well done!


LRCampos.

 

[johara1]

I can not see this happening, you can not know for sure what the group that is shot at 300 was the the same size as the group you shot first at 100 . I feel you can not be proved or disapproved because it can not be done at the same time. To shoot through something no matter how thin would dilute the findings. If a bullet is so out of tune to yaw at 100 no basis for any findings……. It is a cone of dispersion………in my 55+ years of shooting i never saw it happen …... jim O'Hara

 

[m500]

I have to agree with Jim on this. I think anything contacting the bullet on the first plane would effect its trajectory and place of impact on the second, rendering the test invalid. Such a test would need some type of acoustic system or other means of mapping bullet "placement" on the first plane.

 

[Bryan Litz Ballistics]

It's been well established that screening groups in this way does not affect their flight in a signifficant way.

Prior to spark ranges in ballistics labs, they used 'yaw cards' to record the orientation of bullets in flight. Some set ups had the bullet passing thru dozens of these cards, and their presence did not alter the flight dynamics signifficantly.

On all of my shoot thru targets, it's evident that the 'shape' of the group at 300 yards is a direct 3X enlargement of the group at 100 yards. If the paper were deflecting the bullet, this would not be the case.

I'm quite confident that the shoot thru target does not invalidate the test. A well calibrated acoustic target would also work, but IMO it's overkill for the task at hand.

LRcampos,

1) The target I posted is but one of many examples. I've got a lot of sub 1/2 MOA groups thru the set-up, and the same pattern is evident (300 yard groups are 3X the size of the 100 yard groups, and the same shape).

2) I take your point that my set up isn't looking at effects beyond 300 yards. Many/most of the accounts of observed group convergence are between 100-200 or 100-300 yards. Beyond that, conditions get involved to a greater extent and make it more difficult to know what's going on. On a different forum, a guy set up a 100-600 yard shoot thru for his rifle that typically groups ~2" at 600 yards, but averages 3/4" at 100. When he set up the shoot thru aiming at 600, he got his typical small group (something like 3") at 600, and, to his surprise, the smallest bug-hole the rifle ever shot at 100! He was totally expecting to see 3/4" at 100 but the bullets didn't fly that way. Regardless if we look at it from 100-200, 100-300, or 100-600, if something strange is happening, I think it will be detectable between any two ranges.

-Bryan

 

[Jay Christopherson]

I can not see this happening, you can not know for sure what the group that is shot at 300 was the the same size as the group you shot first at 100 . I feel you can not be proved or disapproved because it can not be done at the same time. To shoot through something no matter how thin would dilute the findings. If a bullet is so out of tune to yaw at 100 no basis for any findings……. It is a cone of dispersion………in my 55+ years of shooting i never saw it happen …... jim O'Hara

I have to agree with Jim on this. I think anything contacting the bullet on the first plane would effect its trajectory and place of impact on the second, rendering the test invalid. Such a test would need some type of acoustic system or other means of mapping bullet "placement" on the first plane.

I disagree - if the test is run a sufficient number of times and produces results that are both predictable and repeatable, then it most definitely represents empirical proof, IMO.

 

[LRCampos]

.

Well, if you shot others targets with more accurate loads and it showed the same correspondent patterns at 100 and 300yards, so I think you have a good point on it.

Anyway, I tend to believe that groups are a cone of dispersion... or at least I dont understand why it would group "smaller" at longer ranges than short ranges (change directions of bullet flight inside the cone).

Thanks!


LRCampos.

 

[Romulus]

I know this thread is not intended to posit theories and mumbo jumbo, but I want to thank you for taking this up as I regularly hear and then discuss this stuff when I find myself on a public range. Also, I want to subscribe to this and see what others have to say

I find it interesting that the most common group that believes this (in my run-ins at least) is the magnum or supermagnum crowd with 7 STW, 7 Rum, 338 Super Mags, etc.

I believe this is a psychological/physiological phenomena much like stringing or like performance anxiety as mentioned in the first post. Zoom out a bit where you are only focusing or have access to focus on orientation and more singular aiming detail and - VOILA! - small groups without stringing!

Perhaps a "quasi"-experimental setup to test the other side of this coin would be to take shooters who observe this non-linear dispersion happening and enlarge the aiming area to a consistent size throughout ranges or show high target detail proportionate to that of shooting at 100 yds. Of course a psychological experiment would take more subjects, time, and be messier than your physical results "blind" experiment - which I see as the most straightforward and unconvoluted method possible.

Again thanks for contributing so greatly to our sport. Since I started shooting you have revolutionized the scene for many of us and instead of stopping you keep up with that leadership and keep improving components and education.

Thanks for being so patient with all of us non-aerospace engineers lol! ;D

 

[CatShooter]

I looked at this some years back on a challenge from some members of a local shooting group.

There are several problems with the "theory" of non-uniform bullet travel.

1 - If the bullet leaves it's axial path and starts to travel in a helix, there is no mechanism to bring it back "on line" so to speak. To the spinning bullet, the world in front of it is a blur, and there is no way it would know when to turn back, and in which direction. There are no "lifting" surfaces that could or would cause it to fly in a circular helix - it would enter destructive precession.

2 - If a bullet, like the 175 SMK leaves a 12" twist at 2,600 fps, and makes 1" groups at 100 yards due to helical motion, then the motion is composed of a forward motion, and a circular motion. The radial force to keep the bullet in orbit around the axis with a 1/2" radius at 2,600 rps, or 156,000 rpm, is (ready for this...) over 15,000 linear pounds!! There is no way such a force can be existent in this situation. There is no source and there is no anchor.

3 - We built a 10 foot box, and spaced tissue thin rice paper every 6 inches through it, and used it as a shoot through box at 25, 50, 100, and 200 yards, looking for a helix - we use a laser to check alignment of the bullet holes - in all cases, the holes were in perfect alignment.

4 - Then there is the physics of it - the only motion that effects bullets is precession - the others like yaw are dampened so quickly (within an inch or two), that they do not enter the calculations.
Once precession starts, there is no dampening or correcting force - the off axis angle of attack causes the precession to increase, until the bullet hits the target sideways.

The two cases of non-linear bullet travel that I saw, were due to parallax... much to the embarrassment of the owners who swore that they knew how to adjust a scope.

 

[m500]

Bryan, are you looking more at horizontal dispersion, vertical dispersion or both in this testing? I'm assuming (stupid I know) that you are looking for a horizontal anomily, as a vertical anomily should/could be much easier to explain.

 

[B Mize]

Reading this made my head hurt.

 

[Shortround]

Bryan,

This discussion could get interesting. While the attached discussion was about bullets "going to sleep", the dispersion "issues" also came up. It's interesting.
I was going back through some of my archives and came across some discussions along the same lines, only 20 years ago. I'm going to post some of them here. some of the names I recognize. Hope none of it is copyrighted, if so, I apologize.

I will add that an old Gunner friend summed it up this way;

Kinda hard to explain what all is taking place, but to sum it up "there's a whole lot of "stuff" happening all at once". He described the projectile flight path as a long wavelength, decreasing frequency, variable amplitude corkscrew.

I'll see if I can find his write up. Lots of engineer/physicist speak translated by an old gunner of 40+ years’ experience.


From: sfaber@intgp1.att.com
Subject: Re: [RIFLE] [RELOADING] Load development
Organization: AT&T

From article <CHB6MA.FE7@fc.hp.com>, by bartb@hpfcla.fc.hp.com (Bart Bobbitt):

Todd Enders A262 857-3018 (enders@warp6.cs.misu.NoDak.edu) wrote:

Indeed good advice. One of the raps against 6.5mm cartridges, especially with 140 gr. bullets is that "they don't group" at 100 yds. However, if tested at 200 or 300 yds, the groups, on an M.O.A. basis are *tighter* than at 100 yds. The bullets just needed a little time to "settle down" in their trajectory.

I've heard for many years of these `raps' with just about all bore sizes. So some time ago, I did some tests to find out what causes this `wait until they settle down [go to sleep is a common expression]' philosophy. When bullets were fired at muzzle velocities fast enough to spin them too fast, they always grouped smaller in MOA at longer ranges than shorter ranges. When fired just fast enough to spin at the lower end of their required RPM range, groups were equal in MOA through 300 yards or thereabouts. Groups did enlarge due to velocity spread and time of flight which is what the laws of physics predict.

I read a similar account in Handloader recently where the author tried to answer a question about overstabilization. He mentioned how complicated it was and then proceeded with the bullet going to sleep story. I still couldn't figure it out. The bullet should become more stable due to the decreased drag down range, and the bullet is more stable if spun faster initially, so what makes it group poorly at short range? It sounds like the story is that an overstable bullet is actually spiraling in initially where a marginally stable bullet isn't.
I guess this may make sense if the precession rate of the bullet is slow enough so that it is laterally displaced resulting in a spiral path. The precession rate will be proportional to the drag divided by the angular momentum along the spin axis, so if this angular momentum is high (high spin) the precession rate could be low enough to cause this in an "overstable" bullet where in a marginally stable bullet it would precess
too fast to notice the displacement.

Steve


________________________________________
From: sfaber@intgp1.att.com
Subject: Re: [RIFLE] [RELOADING] Load development
Organization: AT&T

From article <CHJ0pn.16w@fc.hp.com>, by bartb@hpfcla.fc.hp.com (Bart Bobbitt):

That's exactly what happens when a bullet is spun a bit too fast when it leaves the barrel. Its centrifugal force is just enough to cause it to wobble, but as soon as its spin rate slows down enough to where the centrifugal force no longer causes it to wobble, it will fly point on quite well. During the time the bullet wobbles a bit and its axis isn't tangent with its trajectory, it presents different attitudes to the atmosphere it's flying through, so it tends to take a spiraled path to through the air. When its RPMs are a bit lower, it now flies straight through the air in a much straighter path. OK, I understood your theory of unbalanced bullets and over stabilization, but I was thinking of the perfectly balanced bullet case.
Even a perfectly balanced bullet will wobble - precess and nutate to a greater extent according to the drag to spin ratio.

Does Mann's book show a spiraling path to the target? How big a spiral? Does the spiral increase and then converge, or does it just diverge? What would the nature of the forces be that would make it converge again if it does? If it diverges for a while and quits, then it seems that the observed divergence would just be worse at long ranges, unless the spiral is totally reproducible.

I was brushing up on the chapter on motion of a rotating projectile in Moulton's book on Methods of Exterior Ballistics (1920s) where he did the theory associated with experiments similar to your Mann's with projectiles fired through cardboard screens. Moulton discusses the firings of 3" projectiles at Aberdeen Proving Grounds.
He does not address any translational motion or spiraling in his theory except for drift due to rifling twist, and only deals with measurements of the angles and periods of nutation and precession and how these damp out with time. Here is a summary:
He derives the gyroscopic motion of the projectile and defines a quantity "S" that is inversely related to the rate of spin (or stability). The value can approach 0 as the spin increases, and can reach a value of 1 where it is at the verge of total instability. (It is also proportional to the torque on the bullet by the wind drag.)
The bullet's spin axis will make a small angle "theta" to the bullets path that will increase and decrease between 2 values, theta1 and theta 2. This action is called nutation, and its period "P" is calculated and varies with "S" and the initial conditions which determine the initial angles. Good projectiles and guns give small initial values of theta, so the result for the nutation period is P= tw/(v*sqrt(1-S)) where tw is the twist length and v the velocity.
Then there is precession where the axis sweeps out a cone shape around the bullet path line. The bullet is found to transition between different modes of wobble, a fast precession where the axis sweeps a about 360 degrees each nutation period, and a slow precession where it only sweeps a fraction, typically 1/4 a circle each nutation period.
There are 3 modes of this slow precession which vary by the way the precession speeds up or slows down on each nutation bob (the precession is not a constant speed).
Next - how are these oscillations damped? Even if the velocity and S were constant and the bullet moved in a straight line, the oscillations would be damped in the following manner: The fast precession mode would have theta1 and theta2 both decrease and merge together resulting in a more stable configuration with the bullet pointed where it is going. The slow modes would have theta1 and theta2 merge but increase, resulting in a less stable situation.
Now add in the effect of changing v, S, and the effect of a curved trajectory on the damping and the result is that all modes have theta1 and theta2 approach each other and decrease toward stability.
The rate of this damping is expressed as an equation, but I have not figured out how to calculate the coefficients quantitatively yet. It is shown that a bullet will follow the path of its curved trajectory so that theta(1,2 merged) remains a constant or decreases due to increasing S downrange.

Overstabilization is discussed only in terms of a bullet where S is too low a value to allow the bullet to follow the curved trajectory in this manner. If this is the case I would expect to see an effect that would increase down range, but it seems we don't see this in practice.

Steve Faber

________________________________________
From: ohk@tfdt-o.nta.no (Ole-Hjalmar Kristensen FOU.TD/DELAB)
Newsgroups: rec.guns
Subject: Re: Bullet's Angle in Flight
Date: 11 Dec 1997 07:15:03 -0500

bartbob@aol.com (Bartbob) writes:

Over the years, I've heard all kinds of comments, theories and the like regarding the angle a bullet has while going downrange. For example, if the bullet is properly stabilized by its spin rate and is fired at an upward angle of, say 15 MOA (like for a target about 500 yards away), does the long axis of the bullet:

Remain at +15 minutes up angle for its entire flight?
Or
Stay parallel to its trajectory path and point down as the trajectory goes down?
And
Do rifle bullets and larger artillery/naval projectiles have the same characteristics in this regard?

I'm curious to know what others believe.

I have been thinking of the same problem over the years, but I have no really good answers. However, I have a couple of data points, both derived from military experience.

1. I once saw a high-speed film of a projectile in flight, I think it was 155mm, but it may have been bigger. The nose of the projectile was running in a circle around the direction of flight, not very large, but obviously following a corkscrew trajectory.

2. The 107mm mortar is not fin-stabilized as most mortars are, but spin-stabilized. The initial angle of flight is about 45 degrees, yet it comes down with the nose first.

A rifle bullet is governed by the same laws as a larger projectile, but the relative magnitudes between the air forces, gyroscopic effects, and gravity need not be the same. A projectile of large diameter has a much larger moment of inertia, of course, and the ballistic coefficient is larger, meaning that inertia has relatively more influence than the air forces. Nevertheless, if the projectile is properly stabilized, I believe rifle bullets and military spin-stabilized projectiles will show approximately the same behavior.

The reason for this, I believe, is that if the spin is appropriate, the balance between the gyroscopic forces and the air forces is such that the projectile will either tumble, do the corkscrew motion with its nose, or align itself with the direction of flight (which could be viewed as an infinitesimally small corkscrew motion).

The corkscrew motion probably comes from the fact that if you push at a gyroscope, it will respond with a movement in a direction at right angles with your push. If the air forces (drag) tries to push the nose further out of alignment with the trajectory, it will respond by moving the nose at right angles to the push. Thus, it will start to move in a circle. I have not done any calculations, but I would think that after a while (if it is properly stabilized) those small oscillations induced by either a change of direction of fight or any crosswind, will die down, and the projectile will align itself with the new direction of flight. As the rifle bullet is travelling in an approximately parabolic trajectory, the direction of flight is continually changing, so I would expect a very small corkscrew motion at all times, but aligned with the instantaneous direction of flight.

Hopes this makes some sense. I really should go read Dr. Mann before shooting my mouth off, I guess.

Ole-Hj. Kristensen


________________________________________
From: bartb@hpfcla.fc.hp.com (Bart Bobbitt)
Newsgroups: rec.guns
Subject: Re: [RIFLE] [RELOADING] Load development
Date: 4 Dec 1993 21:32:08 -0500

What do you mean by 'spiraling'? If you're saying that it's doing the equivalent of a barrel roll done by aircraft, I can't see the physics allowing that motion of the bullet.

Neither could someone else about ninety-some years ago. So he made some very interesting tests.

Read Dr. F.W. Mann's Book, `The Bullet's Flight from Powder to Target.' It has excellent examples of this. Thin paper sheets placed every few feet between muzzle and 100 yards show the exact spiral path of the bullet.
It even shows how the angle of the bullet relative to its down-range path is determined. Great reading. Even though it was first printed in 1907.
Physics hasn't changed much since then.

BB

________________________________________
From: Gale McMillan <" gale"@mcmfamily.com>
Newsgroups: rec.guns
Subject: Re: Short-range instability ( was RE: The 50 yard Sermon )
Date: 25 Apr 1997 13:22:09 -0400

Stephen Swartz wrote:

Hey Guys:

I can see how aerodynamic effects and the forces created by the center of mass and center of aerodynamic pressure being in two different places on a bullet can cause the "flight path" to be affected.

I'll even buy this spiral flight path thing HOWEVER the great question that was never answered (at least this time around) was:
"But why would the spiral be **different** every time?"

(remember, group size is a function of each bullet following a different flight path; not that the flight paths in general are screwy) In other words, if each bullet consistently follows the *same* "spiral path" around the arc of flight, you would expect to see;
Bullet holes at different relative positions for different distances,
Different group sizes (in moa) the further you go out due to differential environmental effects (wind, etc.)
Different flight paths due to each bullet being different but, not *smaller* (in terms of moa) group sizes!!!

Or are we claiming that the dispersion around the *spiral itself* gets smaller the further out you go????

This wouldn't seem to make much sense. A spiral path in and of itself- even if the spiral gets smaller- may explain how a *single* bullet tends to "home in" on a given flight path BUT does not explain how *successive bullets* follow/don't follow each other more or less closely!

Did I explain this right?
Steve


The difference in muzzle velocity between rounds causes the bullets to go through the paper at close range at different points of the spiral. You will see this more frequently as time goes by due to the numbers of tight twist barrels being used in this fad of shooting overly heavy long bullets. Shoot a 55 grain bullet out of a 9 twist barrel etc. There have been posts in this thread indicating that the dispersion of shots would be in seconds and minutes of angle proportionate to the distance checked. Then I ask why not check everything at short range and eliminate shooter error. We shot 18000 rounds of 50 cal ammo during a contract. The guns were sighted in and function tested at 100 yards and averaged 1.5 moa groups. When these same guns were tested at 600 yards you would expect the groups to run 1.5 moa or 9 inches. The 600 yard targets ran as small as 3 inches and never any larger than 6 inches as an average. Any that shot larger than 9 inches were inspected and retested.
Gale McMillan


Not trying to hijack the thread. Just throwing out some more interesting reading material.

Shortround out

 

[Bryan Litz Ballistics]

Some of these old discussions are linked in a post above.

Much of it is speculation as to what causes group convergence, which is putting the cart before the horse. Remember, all these observations are based on shooting different groups at different ranges, not capturing the same group at multiple ranges. When screening a single group at multiple ranges, there is not a single recorded account of bullets actually flying a converging path.

As for the reference to Mann's book, the demonstration of a corkscrew flight path, as recorded with yaw cards, was under 1 caliber in radius, and it took deliberate mutiliation to the bullet, and/or deliberate disturbance to the bullets departure at the muzzle (plank shooting).

When Mann set up a shoot thru target to deliberately study group convergence, his result was the same as what I've seen so far: proportional dispersion between two distances. His conclusion was that bullets do not fly converging paths.

Thanks for sharing the info though.

-Bryan

 

[Shortround]

After an absence from the shooting arena of some 20+ years, I got back into reloading and shooting in 2010. I am amazed at the technology we now have available to us. When I started reloading back in the mid 60's, we grabbed a can of powder, some primers, a box of bullets, and picked a load range and worked from there till the load shot good. It was simple back then.

Now my loading room now looks like a laboratory. The tools I take for granted now, weren't even dreamed of at our level back then. Technology is wonderful, even tho it has turned an inexpensive hobby into a much more expensive one. However it has been quite the learning experience and that has made this hobby much more enjoyable.

I follow your discussions with relish. I'm glad to see this Ballistics and Bullets Board in here. I'm sure there will be some lively discussions along the way. Out of those discussions will come opinions which will lead to different ideas and more experimentation which will lead to more learning. It's a nice break from trying to make electronic and optical equipment GI proof.

Keep up the good work.

Shortround (Bruce) out

 

[normmatzen]

VERY glad to see you on this forum Brian.

Harry Truman said,"The buck stops here."

I think it is fair to say when you add your 2 cents, "The anecdotal evidence stops here!"

 

[Bob Sebold]

Bryan, I think this myth got started from years ago when gun writers read Hatchers notebook. I read this several years ago and my memory is not what it should be, but I believe he used a 30-06 and fired it through a maze of 1.2 inch dowels. The bullet path enlarged and then grew smaller with distance. Hence the bullet going to sleep theory aka magic bullet. I for one never believed it. I can see all kinds of problems with shooting through 1/2 inch dowels.

I have never had a load that would do what you are asking. I have had 1/4 inch groups that would shout about 2 inches on a rough day at 1000 yards! Maybe, it was me!

 

[wyoming .260]

Thank you Bryan Litz for the information and making me feel half as smart as I did a half hour ago.

 

[Scott Harris]

Thanks for the great post Bryan: love the way you apply statistics and well-thought-out test methodologies to cut through the opinion-based mumbo-jumbo. Your past books have been very useful.

 

[calgarycanada]

So can someone please re assure me here, especially Bryan.
If a load shoots 1/2 Moa at 100 yards, theoretically it should shoot 1/2 moa upto transonic range? Of course I'm removing shooter error and wind here.

When I first started loading, lot of "experts " told me to test my loads at longer ranges(200 to 500) because what works at 100 yards may not work at 1000. But based on this thread if average dispersion of a given load is 1/2 moa it should stay 1/2 moa till it hits transonic range? So can I say it doesn't matter if I develop load at 100 or 300yards, if it groups good at short range it will group good at any range as long as shooter is upto task?