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.

normal?

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.

YMMV ......