Loading a muzzleloading rifle can cause wear to the crown. A false muzzle is a detachable extension of the barrel and bore. The patched ball or bullet is started in the false muzzle then seated into the actual bore with a piston type plunger which aligns with the bore. The projectile is then seated onto the charge, usually with a greased wad or lube cookie separating the powder and projectile. The false muzzle not only holds the projectile in alignment, it can also initiate the engraving process. It may be sized internally to ease entry of the projectile. Wear to the crown is minimized and the projectile is started in perfect alignment with the bore. This is particularly important with an elongated bullet.
Usually a false muzzle will have a blocker which appears in the sights, to reduce the chance of the rifle being fired with the device in place.
The false muzzle will be fitted with pins which engage the barrel. The starter will fit on the false muzzle.
Often when a false muzzle is desired, holes are drilled and reamed, then a piece is cut off and the faces turned flat. The piece is then reinstalled and final reaming and rifling is performed, so that the rifling in the muzzle is exactly in sync with that in the bore.