My AR (Colt AR15-A2 HBAR) does NOT like that ammo. It has a 1:7 twist, so I suspect it's overspinning the bullet (spinning the bullet too fast for its weight). Accuracy at 100 yds is 3-4 MOA.
When I handload 62 and 68 gr bullets, the groups shrink to 1-1.5 MOA.
The ammo doesn't seem to be any dirtier than other ammo, and it cycles my AR just fine. It's decent ammo to get your AR cycling, and relatively cheap, too.
Its bulk ammo, in a SERVICE rifle. 3-4 MOA isn't horrendous, its combat effective which is what the rifle was designed for. Naturally handloads should/would group tighter.
TDC
Bullet weight is the big difference, amigo.
Remember, the M193 round (55 gr) was designed for the earliest M-16's, which I believe had a 1-12 twist.
I'm loading the handload (62 gr) as close as I can get to C77/M855 spec.
You're quite right about the heaviest bullet (68 gr) that I've tried in mine being more accurate.



























