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sleepy bullets and group size

 
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  #1  
Old 02-27-2004, 12:57 AM
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sleepy bullets and group size

OK. Here's one for the hardcore ballistics gurus:

I've heard the theory batted around about some guns having a tendency to shoot somewhat smaller groups proportionally at distance than they do up close. Seems to be more prevalent w/ the long spiky high B.C. VLD style bullets out of fast twist barrels.

I've seen something that certainly looked like that, where I had a gun, in .308 Win, that would fairly regularly shoot say, a 3/4" group at 100yds (0.75 MOA), then 1-1/4" group @ 200 (0.63MOA) and 1-1/2" @ 300 (0.5MOA). Somewhere btwn 300 and 600 the group size started opening up 'normally' to where it was a little over 0.75MOA @ 600yds. I've also followed threads where it would appear that this happens somewhat regularly to others. Even in shooting sports like HP, competitors are often cautioned to do their load workup @ distance, as their best 600yd load may not look that hot @ 300, and vice versa - a load that looks sweet @ 300 may not hold together for the long yard line. Ditto for Palma distances (800,900,1k) compared to 600.

Recently I've encountered a fellow who apparently has access to several Oehler 43's or else has acquaintenances who do, and is quite adamant that there is no way in heck that that could possibly take place, as it's never been documented to his knowledge over 'real' targets in the form of acoustic or radar targets; that the groups always get bigger, *always*. Given the 'anecdotal evidence' as he refers to it of my experiences, I get a lot of talk about unstable bullets making ragged holes at shorter ranges. When I point out that other people have seen this as well, I get some babble about how other people have seen aliens and believe in them as well. So at this point we've just agreed to disagree [img]images/icons/wink.gif[/img]

It does have me curious, though. Have any of you long-rangers seen anything to make you believe one way or the other? I don't really care who is wrong or right, but darn it, if I'm wrong, I *really* want to know what was going on those days at the range [img]images/icons/wink.gif[/img]

TIA,

Monte
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Old 02-27-2004, 01:33 AM
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Re: sleepy bullets and group size

Very Interesting topic,

From what I have seen I would say it is possible for a gun to shoot better in terms of MOA at range. I cannot see where it would be possible to shoot a better group, that would mean that the bullet is making a sidways arc and therefor would really only be on zero in regaurds to windage at one range. But I do think that it is possible to shoot say .75in groups at 100yards and 1" groups at 200 yards and 2" groups at 400 yards. Because I have seen it. I think this happens when a bullet is just on the verg of stabilization. MY gun that does this is a 220 Swift AI. The barrel is 16 twist and I shoot 55gr bullets around 4250fps.
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Old 02-27-2004, 02:06 AM
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Re: sleepy bullets and group size

Milanuk,
I was going to ask you if you were familiar with the Oehler 43's acoustic target, but you went on to actually mention it. [img]images/icons/smile.gif[/img]

I actually have one and am getting ready to run this very test here in less than a week or two. I've got a broken leg of PVC pipe on it right now, almost cut the wires running through the PVC my pistol when I hit it!

I could get set up and test tomarrow if I ran to the hardware store and got another stick of PVC, but it's my Dad's B-Day tomarro and we're already to go and have a bunch planned to shoot already.

I'm fixin to set the acoustic target up at 100 yards, then the target frame at 300 yards to try and lay this to rest for myself, I have seen it happen too. I don;t remember which loads, but it was with a 12 twist 308 and possibly even my 416 wby, but I'll just have to shoot for a while to see what I find. The nice thing about the acoustic target is that it doesn't interfere with the bullet in flight.

It will tell the tale if it happens.

I've shot enough groups with the 210 JLK now that I think it's not an issue with it in my 11 twist, it shoots too tight at 100, and pretty much extrapalates to my 300 yard groups.

I'm not convinced I'll even find anything interesting the first time out trying this, and more than likely it will take seeing it happen at some point down the road then further range tests with the acoustic target to validate, or dismiss it.
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Old 02-27-2004, 08:47 AM
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Re: sleepy bullets and group size

Keep us updated Brent--Im interested too [img]images/icons/wink.gif[/img]

JB
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Old 02-27-2004, 10:16 AM
MAX MAX is offline
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Re: sleepy bullets and group size

There is a very recent and long discussion on this subject on page 2 of this forum, "Bullet Stabilization Question", posted by Wyoming Whisper. It may provide some answers to your question.

The factors at play are fairly complex, and most of the top echelon ballisticians say "No.", but they are looking at it purely from the aspect of bullet dispersion. The one precession cycle that does null in the bullets flight is very small and likely of small influence, but it does occur in the first 200-300 yards of flight. A more likely thing(s) that influences this to my thinking is parallax, changing wind, and variations of load/bullet balance that will occur from one round to the next.

It is likely that this debate will continue for all time as the resoultion to the question involves far too many variables to control. I'm no rocket scientist, but that's my opinion.
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Old 02-27-2004, 01:00 PM
MAX MAX is offline
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Re: sleepy bullets and group size

Luck to you Brent. It is a thing of very fine discrimination that you tackle here. Do you per chance have of of Vern Jeunke's concentricity devices? I'd think sorting the bullets would be an advantage. Wish I had your "facilities" for load testing. Sounds nice. [img]images/icons/cool.gif[/img]
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  #7  
Old 02-27-2004, 01:14 PM
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Re: sleepy bullets and group size

Max,
Yes, I have an I.C.C here too. I'll do that.
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