Well he said stainless, so park undercoat is out. Bead blasting/degreasing would surely make any paint stick better to the steel. I am wondering about high temperatures. It is a semi auto, right? Might get alot of rapid fire some time and barrels on a hot day can get pretty hot. Some kind of paint that is hi temp rated might be advisible in that case? Maybe some of the stuff you bake on. That makes it durable, and if it can stand baking, it could stand a hot barrel, I think?