There are many good ones. Teflon, Parkerizing, ceramic, bake on expoxy, and we are now using epoxy powdercoat. What we do on the SC rifles is coat the bolt (internal) in black teflon to insure smooth operation. Then we use expoxy powder coating on all external parts. Supposedly ceramic is about 3 times are hard as powdercoat, but then again, its 3-4 times as expensive.