Rifle muzzles are usually crowned to minimize turbulence at the muzzle.
Gun muzzles are “crowned,” or angled away from the center of the muzzle, in order to minimize turbulence at the muzzle. Crowns give burning powder and propellant gases a place to go that is not in front of the bullet. By convention, most muzzle crowns are cut at an 11-degree angle from square. There does not seem to be an empirical reason why the crown cannot be 10 degrees or 12 degrees. If you have the right tools, there is no reason why you cannot cut and crown a rifle barrel yourself.
1. Wrap the end of the barrel with masking tape. Draw a pencil line where you intend to cut.
2. Put a metal miter box on a workbench. Put the barrel in the miter box and align the pencil line with the 90-degree cut angle in the box.
3. Immobilize the barrel, or firearm, in the miter box by fastening the barrel, or firearm, to the work bench with two padded C-clamps.
4. Insert the blade of a hacksaw into the 90-degree cut angle in the miter box and saw until the barrel is cut completely through. Remove the C-clamps. Remove the rifle, or barrel, from the miter box.
5. Remove any burrs or rough spots with a fine, flat file. Generously apply cutting oil to the new muzzle.
6. Attach an 11-degree reamer to a large tap handle. Insert the reamer into the muzzle and deliberately turn the reamer until the desired crown is achieved.
7. Polish the new crown with fine emery cloth until the crown is completely smooth.