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saboteur
June 8, 2009, 12:00 AM
I have a Auto Ordnance Tommy Gun with a threaded barrel. I ordered a Cutts compensator with included front sight from the manufacturer (also with threads).

When I screw the compensator onto the barrel, and it hits the end (i.e. is on tight), the front sight post is nowhere near where it is supposed to be.

Any ideas for a fix?

Slopemeno
June 8, 2009, 12:28 AM
It needs to be "indexed". A small amount of the rear of the comp needs to be turned off to allow it to stop *just* short of 12:00. The Cutts compensator is then snugged on the last bit to get it on solidly.

saboteur
June 8, 2009, 12:54 AM
Great! Is this something that your average competent gunsmith would be familiar with?

Dfariswheel
June 8, 2009, 07:18 PM
Depending on the version and age of your semi-auto Thompson, the compensator was either epoxied or cross-pinned in place.

The newer Kahr-Auto Ordnance versions seemed to use the pin-type of mount as used on the original Thompson SMG's, at least for a while.
The semi-autos made by Numrich-Auto Ordnance, and the early Kahr-Auto Ordnance guns simply attached the compensator with epoxy glue.

Turning the rear of the Thompson compensator doesn't work. The muzzle is not threaded with a positive stop, and the compensator will simply keep turning until the muzzle contacts a ledge inside the comp.
Turning off the rear of the comp has no effect on indexing.
There's no way to get to that internal stop easily to index the comp.

So, either do as the original semi-autos did and use epoxy, or buy a surplus or Kahr-made pinned comp and cut a pin groove on the muzzle threads.