Originally Posted by Majorlk

1/4 or 3/8 half-cut mill file. Depth is controlled by pressure on the file - press down harder, cut deeper. It doesn't take much. I actually cut a 1/16" deep slot in the underside of the barrel so it would be impossible for the set screw to slide across the barrel.

I mounted a TactiCool threaded barrel adapter on the barrel and a Tactical Solutions muzzle brake/compensator on the adapter.