On another fourum, a respected and experienced shooter has assembled 2, 300 BO uppers, and can not get better than 2.5 MOA…at 50 yards (5-6 @ 100) either suppressed, unsupressed, and bare muzzle. His 16" 300 gets just over 1 MOA @ 100. All have SureFire muzzle devices and suppressors, properly installed and torqued.
He has a 5.56 SBR that is getting sub MOA at 100. It’s not the shooter. All four uppers have been tested with the same optic/mount and is repeatable after switching out.
He has tried 5 different brands and bullet weights in both SBR uppers, no change.
Barrels are a 10.5" AR Stoner, and an 8" CMMG. Both have 1:9 twist rates.
Crown is good on both. Barrels are square and tight.
300blk needs a 1:7 or 1:8 twist for a sbr. Shooting a 110gr to 220gr projectiles they need to rotate faster. I have never heard of the stoner barrels being very accurate period. No experience with CMMG personally but I have assembled a 12" CMMG upper for a friend and he is reporting 1.5" groups at 100yrds with Remington 120gr (made by Barnes, in Barnes brass and Barnes bullet packaged in a Remington box).
Subsonic is tough to be very accurate. Supersonic is no problem. I shot this at 100 yards with no magnification. Then I did it again with an Eotech with about the same results.
It’s all been quality ammo, different weights of the same brands, and IIRC even some subsonic (all others were super). NOTE - correction on the twist rate. Both uppers are 1:7 twist.
He’s tried everything on theses uppers to diagnose it, and I think he is probably down the the barrel MFGs as the problem.
