Bullet Stabilizes at range but not close...why?

rem.xp100

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Joined
Mar 30, 2005
Messages
58
A 10 shot sub quarter moa group with a 300 win mag In a hunting weight rifle is beyond incredible I’ll just say that.
+1 Phenomenal shooting and rifle for sure.....I would have been impressed with sub half. As to the original quandary, my thoughts are operator and conditions rather than the rifle/bullet doing anything strange.
 

Tumbleweed

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Joined
Oct 20, 2007
Messages
610
Location
Tillamook, Oregon
Check your seat belt and cover your popcorn....it's gonna be an E ticket ride....... This phenomenon does not occur in true BALLISTIC CONTEXT per Bryan Litz as presented in his Applied Ballistics Seminar.......CUE THE PEEPS IN THE PEANUT GALLERY TO GO WILD!!!!!! All info is credited to Bryan Litz, Applied Ballistics,.....questions [email protected]. I am not stealing, plagiarizing (aka "Bidening"), just sharing what my $650 and 1350 mile (one way) one week road trip temporarily tried to teach this old guy. This perceived phenomenon is GROUP CONVERGENCE......when the group doesn't disperse in a natural linear fashion........the group MOA appears to get smaller at increased distance. One theory for group convergence is the "bullet going to sleep." Yaw vs Pitch relation dampens from barrel to down range becoming apparently more stable flight. Effects are self dampening resulting in very little steering effect......only about 1/10 caliber. POSITIVE COMPENSATION, possible only in the vertical plane, is another popular theory where higher velocity shots exit the muzzle pointed lower; slower shots exit pointed higher. Groups tend to be larger at short range - 100yds, converging at longer ranges - 600yds This occurs more often with less rigid barrels/action; less with stiffer/bull barrels.

Issues with studying convergence via live fire is need to screen same group at multiple ranges to directly observe convergence.....hence, the shoot-thru target tests. His extensive testing experience confirms zero effect of paper punching on ballistics. (I refer you to his address above.) Bryan presented numerous sleep inducing pages of data involving marginal/low stability, switch barrel caliber variation, aim point size versus distance to target, various combinations ad nausea, measuring and plotting Convergence Ratios that only a real Rocket Engineer (that he was before Applied Ballistics life) could or would want to understand.

Conclusions: The average convergence ratio for all testing was 1.16. There was no rifle/bullet combination consistently producing a CR under 1.0. He could not identify any direct physical evidence anywhere that convergence occurs demonstrably, repeatedly with center fire rifles, outside the previously mentioned mechanisms.....positive compensation, yaw/pitch. Even low stability cases exhibiting poor groups showed CR about 1.0.

Bottom line, the strongest connection between distance and angular group size was found to be related to the size of the aim point, making perceived convergence an optical, or psychological issue rather than a ballistic characteristic.

Bryan summarized that the belief in convergence has prevented the trust in load development at 100yds. But, the importance of understanding aiming is important. Summarized as Aim Small; Miss Small., or a parallax effect.

You may open those pop corn boxes at will. Class dismissed. Let the flaming and self-pontification commence.
That's interesting, I have a ton of respect for Bryan too. Whatever may be the cause of this perceived (or real) phenomenon, I've dealt with it for years and the reason I only do load development at 250 yards or more. I've worked up loads at 100 yards (even less as per an experiment suggested by a friend) and they never held at distance. Done in reverse, accuracy and consistency beyond 300 yards has been excellent (half moa or better) and groups inside 200 yards mediocre to poor (1 moa or worse). I've always attributed it to bullets needing to go to sleep over a couple hundred yards. Whatever the cause, this has been my remedy and I try not to overthink it, just do what works for me.
 

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