If it's Rocksett this method is supposed to work, found on another forum.

1. Boil water in a pan, submerge mount/threads into it and leave it overnight. Try not to leave too much of the barrel in there if you can help it, though it won't hurt if you clean it good later.

2. In the morning or next day, do this again. Leave it in the water for ten minutes or so to heat back up but before the water is cool, remove it.

3. Have your reaction rod or barrel vise setup and quickly put it on (for removal).

3. Should wrench right off now.

A little heat from the torch can help, but only after you've soaked it like this. It'll "crack" easier like the guy above said if still stubborn. This is what works best for me. Quickly clean it with a brush and pick after it comes off and before it rehardens and it'll be much easier to clean. Be sure to get it all out then.