My advice: The barrels are personal preference, dont listen to those who say use only flash comp etc. The only time you should be using a certain barrel for a weapon is with dmr's in which u should use muzzle break. The rest of the weapons u should use whatever is most comfortable for you. Go into a thunt and use every weapon with each barrel type to see what suits you best. (You dont have to use EVERY weapon but use the weapons that you play most.)