Heres one more. Take a bullet of the same caliber, and slightly tap it into the muzzle end point first. I know what a lot of you are thinking right about now. The crown!!! The bullet has a cooper jacket. The barrel is steel. You're not going to hurt anything. The Bullet will create a perfect seal, and no Cerakote will get where you don't want it, plus it really protects the crown from blasting.
BTW, I mean just tap it in slightly, not drive it in passed the ogive of the bullet. So don't use a BFH.