I am fairly certain this is rust:
Can I get an A2 swapped out for an A2?

Some WD-40 and a hard bristly brush should remove whatever that is.
Originally Posted By bigbore:
Some WD-40 and a hard bristly brush should remove whatever that is.
Brass or nylon bristles?
spray, scrub, blue.
I avoid shooting mine because that part tends to get really dirty

Originally Posted By an_hero:
I avoid shooting mine because that part tends to get really dirty

Dirt, carbon, and crud are just fine with me. Corrosion is different.