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

Idaho Hunter1

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May 5, 2019
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Boise, ID
So here is the question: Why could I have a bullet shoot sub quarter MOA at 100yds then grow to 1 MOA at 200yds and then shrink back down to .5MOA at 300yds and 500yds. Rifle is a quality custom build in 300 WM and using Accubond bullets. SD and ES are single digit and I think I’m happy with the performance but never seen this personally. All the groups were 10 shots each so I feel pretty confident this is not a fluke.

Bullet weight is 200gr, velocity is 2900fps, twist is 1/9.4.

Thanks
 

P7M13

Formerly 'P7id10t'
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Orygun
Was thinking the bullet might be doing the macarena as it flies to the target.

Set up a target at 200 and 300, shoot through the first target into the second, you will then be comparing the same 10 shots at 2 distances.
Though the effect of hitting the paper may be discarded as insignificant, it will still affect the trajectory and possibly invalidate the findings.
If you have access to electronic scoring systems, see if you can set them up at successive distances to look at bullet target path. A 36" window should give you ample area to handle trajectory arc across the distances.
 

LaHunter

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N.E. Louisiana
Just my opinion, but I would say it is likely not the load. It is most likely operator influence, parallax, wind, lighting, or any other variable. A 1 moa group at the closer distance can't become a .5 moa group at a further distance. Sometimes at further distances, we relax more and just execute the shot vs tensing up and 'trying too much' to stack the round on top of each other at closer distances.
 

Axl

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Was thinking the bullet might be doing the macarena as it flies to the target.


Though the effect of hitting the paper may be discarded as insignificant, it will still affect the trajectory and possibly invalidate the findings.
If you have access to electronic scoring systems, see if you can set them up at successive distances to look at bullet target path. A 36" window should give you ample area to handle trajectory arc across the distances.
The "shoot through challenge" was something Bryan Litz from Applied Ballistics came up with in 2015 or so. Here is a quote from him on the subject of the first target affecting bullet flight:

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.
 

Idaho Hunter1

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Boise, ID
Let’s assume that the shooter and the environment were not causing ill effects. Could it be something as simple as the physical distance between impacts at 200 yards and 300 yards are the same for some reason related to rotational stability as the bullet slows some?

I have not had this problem with this rifle while shooting factory 178gr Hornady ELD-M side by side. I shot those shots with that ammo as a control group to see if I had a rifle that had become fouled somehow.

Not trying to cause a argument as much as understand if I can trust this ammo to hunt with. I wasn’t sorting bullets by measurements and weights before loading them, just using all components from the same lot.

If no one has experienced this, my plan would be to just work some more up and try them all the way out to 1k and see what comes of it.

And I’ve read the Litz theory papers and would agree, I just can’t argue with holes in paper and on steel.
 

timeless61

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Nov 18, 2008
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Look into positive compensation. It may not be what you are experiencing or evident at shorter distances, but still good to read about. There will be more information on accurateshooter.
 

Shadowwalker

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May 23, 2018
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94
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GiLMER TX
Just my opinion, but I would say it is likely not the load. It is most likely operator influence, parallax, wind, lighting, or any other variable. A 1 moa group at the closer distance can't become a .5 moa group at a further distance. Sometimes at further distances, we relax more and just execute the shot vs tensing up and 'trying too much' to stack the round on top of each other at closer distances.
Ever hear of conditions?
 

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