I want to find out if you could shorten a barrel on a semi auto Thompson and have a permanent cutts compensator? Like the way Bushmaster sells M4 uppers with a 14 inch barrel and permanent FH. At least then with the Thompson it would look a little closer to the FA gun.Another reason is why would you take the comp off except to replace it? Thompsons don`t look right with any thing else.

Is it possible to replace the semi-auto Thompson barrel with a GI one once it is registered as an SBR?

How well do the new Thompsons work?

Av.

Shortening Thompson barrels won't work.  The end of the barrel is expanded into an enlarged muzzle which is threaded.  The M1/M1A1 Thompson's also have an enlarged but  unthreaded muzzle to accept the non-Cutts front sight.

If you cut the barrel off, it's too small to attach either a Cutts Comp or a M1A1 front sight.

Thompson semi-auto guns have the same threads as the full-auto guns, so barrels interchange.
I don't think Kahr changed this.