It doesn't HAVE to be a brake... It can be as simple as a piece of tubing. Doesn't have to screw on. Doesn't have to be rifled. You could make one out of a piece of mild steel, that would slip over the end of the barrel, and have it soldered on. How big the inside hole is, would be up to you. The only reason this comes to mind, is that once I salvaged a too-short shotgun barrel (by a 1/2"!) by silver soldering on a piece of tubing. It weren't pretty, but the guy didn't have to buy a barrel for his old single shot! He went away happy.