When we took the barrel out on week two, all groups were better. The best was a hot 55 gr game king load that I'd put together last year some time.
It also shot the 77 gr house load MUCH better, but not quite sub MOA. The barrel is spaghetti strap thin, and we have a Sig can hanging on the front of it, so harmonics may be super sensitive.
"What would a $2,000 Geissele Super Duty do that a $500 PSA door buster on Black Friday couldn't do?" - Stopsign32v
Faxon, so I assume it's nitrided/QPQ? The twist rate theory and your harmonics theory have merit, but it is possible the barrel may just need several hundred rounds to settle in. I have seen and experienced this several times with nitrided barrels. The surface is so hard that the imperfections take many rounds to smooth out. For this reason, it's common for precision barrels to be hand-lapped or fired a few times before being nitrided.
You're likely aware of all this... Send another couple hundred rounds through it and test again? Curious minds want to know.
I am curious: wouldn't barrel length and resulting velocity interact with twist to produce rpms necessary to stabilize a bullet? Faster bullet as it leaves barrel = higher rpm?
Recognize gun to gun, barrel to barrel diffs and admit I have no experience with short barrels. Little experience with ar.....
But?
This is correct. The stability is a primary function of the bullet rotational RPM, and that results from a combination of both twist rate and muzzle velocity. However, the difference is not that large even for significant changes in MV. You can play with the calculator here:
http://www.bergerbullets.com/twist-rate-calculator/
And get a good sense of it. Berger's 77gr OTM was still stable in a 1:8 at just 2200fps MV, per this calculator.
I suspect that the new barrel and pencil profile are the main issues.
We are hopeful that the barrel needs to settle in with more round count. We brought this up as a potential causative factor. It would be truly stunning if this barrel goes from 5 MOA to MOA with round count. I bought some premium ammo from Bonefrog, we have some 69 SMK's to try and we have Black Hills 77 and 69's to try. Very excited to try the BH fodder.
Barrel twist is but one factor in stabilizing bullets. I have a 1/9 Rem 700 5R bolt gun that shoots 80 grain SMK's light out. It is the most accurate gun that Mark or I have ever shot. There is a great sticky on this about barrels if i'm not mistaken.
I am committed to make this barrel work, I have too much $$ in the gun and SLR gas block that won't fit any other barrel I own. This is the skinniest pencil I have ever seen. The gun handles very nicely. I'll get Mark to post some pics since I'm Photo challenged on M4.
Last edited by Pappabear; 01-26-18 at 10:26.
"Air Force / Policeman / Fireman / Man of God / Friend of mine / R.I.P. Steve Lamy"
"What would a $2,000 Geissele Super Duty do that a $500 PSA door buster on Black Friday couldn't do?" - Stopsign32v
The Remington 700 Barrel is how long?
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