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Old April 26, 2006, 09:06 AM   #26
Jim Watson
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Bullet94

Thank you, thank you, thank you.
I have been looking for a report like that ever since I first read of the Oehler accoustic targets. We can now put the fable of bullets "going to sleep" to bed, so to speak.
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Old April 26, 2006, 02:33 PM   #27
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As Ribbonstone said, this can happen. Usually the group opening is along a single axis, and usually it is the vertical axis. The cause is illustrated below. Unfortunately you need a third range to verify this is what is occurring. It is thought to explain why some loads appear to the shooter to need time to "go to sleep". It presumes some amount muzzle velocity variation, though ignition inconsistency can also cause it.

Note that this comes about because the barrel harmonic vibration is additive to muzzle rise on an upswing of muzzle angle and subtractive on the downswing. Presumably the same thing can occur vectored along diagonals or due to rotational harmonic vibration around the bore axis. Barrel harmonics depend on mass distribution, unlike Chris Long's acoustic pressure wave, which depends only on barrel length. Thus, in some guns, the acoustic wave sweet spots will coincide better with harmonic stringing lulls than others, causing some sweet spots to have wider charge latitude than others. Some gun/load combinations don't show the pre-flat-spot hump in an Audette ladder. These guns are simply better behaved and it is good fortune to have one.

Nick

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Last edited by Unclenick; April 26, 2006 at 09:35 PM.
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Old April 27, 2006, 04:44 PM   #28
30Cal
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Something to keep in mind. When you tear the rifle down and clean it, it may take a couple shots for everything to settle back in place (so if you shoot 2 three shot groups then move to 200yds, those first 2 groups might not be so hot). The less obtrusive you are in cleaning, the less you'll have to deal with this.
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Old April 27, 2006, 10:21 PM   #29
garryc
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Smaller groups at 200 than 100 moa wise is normal. Smaller group size makes me tend to think you have paralax problems at 100yd.
agree 100% most big game scopes are parelax free at 150
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Old April 30, 2006, 02:48 PM   #30
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If parallax is the problem, a good simple explaination of it and how to tell if you have the problem and the corrective adjustment's purpose is here.

I was also re-reading Harold Vaughn's book last night. He suggests indirectly that it may be possible for muzzle blast effect to bear some responsibility. If it does, you could tell by shooting both slow and fast powder loads to the same velocity. The problem would be worse with the slow powder.

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Old May 2, 2006, 06:08 PM   #31
JD 500
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Range Report

OK. the 1/2" groups at 200 must have been a FLUKE.
Could not duplicate or even come close.

Have new post in Art of the Rifle looking for advice on how to learn proper long range shooting / shooting technique.

Thanks
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