When I was heavy into Cowboy Mounted Action Shooting, which uses .45 caliber black powder blank cartridges in single-action revolvers to bust balloons from horseback, I had a Colt Single Action Army hard-chromed by Ford's. All of the firearms (revolvers, shotguns, and rifles) take a lot of abuse from the black powder, especially the pistols as they are used the most. I found the hard chrome (I specified bright chrome) made cleaning the revolver much easier, and you could even wait awhile before cleaning without having to worry about corrosion. I never had any yellowing or chipping of the finish, even in the bore and chambers. If hard chrome will withstand the abuse of high-pressure 5.56 ammunition in the chambers and bore of automatic weapons, it should work for you.