The purpose of a crown is to protect the end of the barrel from damage. The barrel end is very critical to accuracy; if it is not prefect, the bullet will exit one side before the other and be thrown off by the escaping gas on the side that it exits first.
There are tools to cut crowns by centering on a stud in the barrel; crowns have also been cut with a drill bit, or with a round-head bolt and grinding compound. Such methods can sometimes result in a decent crown, but the best way to cut one is on a lathe, using the proper lathe tool.
Many guns, especially target guns, have no crown since the factory thinks the cut end will be more accurate than a crown and that such a gun is unlikely to be damaged. If a gun that has no crown shoots well, I would leave it alone. Sometimes, though, damage can be repaired by cutting a crown or by deepening one.
Jim
to clean.
