recently i have noticed increased copper fouling on a 16" AR
copper is gathering on the slits of a phantom and on the bolt in the area under the gas tube vent.
55gr wolf, been happening for about 1,00rds
Use some copper solvent to remove it. If you have a chrome lined barrel, don't leave it on too long though. Use the solvent until the patches stop looking blue, then some dry patches, then clean as you normally would. I use copper solvent after every time I shoot, but I am anal like that. Most of my shooting is with corrosive milsurp ammo out of 50+ year old firearms, so I clean the best I can everytime. For me,it is better safe than sorry. In a AR unless it is affecting accuracy or functioning, it is probably not too big a deal.