Many times, rebarreled lots of Mini's, Why would you shorten the barrel? that makes no sense. I said turn it, as in turn down the diameter, the same as the first step of muzzle where the sight is but back further so the front sight is back so the end is exposed for the threaded brake. The whole process only takes about a half hour in the lathe, if you are trying to do this by hand good luck. I make my suppressors with a smaller than typical AR thread, but there are several after market ones out there that will work.