I got an AR15 upper in trade a few years ago with a little "ding" right on the muzzle crown. I saw this and planned to someday have it recrowned by a gunsmith. Accuracy suffers (I assume) because of the "ding". Brownells has a hand tool to cut an 11 degree crown in the muzzle. For not too much money. or Remove the barrel from the upper and ship it to a gunsmith with a lathe to do the job. I hate having parts laying around for a couple of weeks. I also have an older Westernfield 22 WMR that would probably benefit from a crown job too with the hand crowning tool.