carbon build up with muzzle attachment
i have a custom .308 with a phantom flash suppressor. when i first started working up loads, it would pretty much shot .5 MOA at 100 yards. 60 rounds later, the groups are now opening up. proper barrel break-in was done. i took the suppressor off to see if carbon was building up. there was carbon on the crown, but not an excessive amt. could this be the problem?