Powder coat would be really tough to get inside either part, but the muzzle would be pretty much impossible. I have not had good luck with powder, once it chips, it keeps coming off.
Cerracote application depends on what kind of air gun you are using and how good you are at it. Inside the tube would be doable, inside the muzzle...pretty tough. If you really really really want it done, dip it. It'd be thick, but what the hell. Cerracote is way better for staying on.
Either material is going to come off the inside of the muzzle brake. Powder particles moving at three thousand feet
