The Kahr L drum I have works well, as does a pre-'94 ban West Hurley L drum. I used to have a Taiwanese made L drum that also worked well and may be lower priced than the Kahr drum. If you don't mind turning $35 of ammo into smoke and noise with a single trigger pull; I do not have one, but the Taiwanese made C drum also gets generally, but not 100%, favorable reviews.
As for cleaning a Thompson compensator, the screw driver scraping and dental pick picking mechanical force tactics were what I used. I did not have much luck with a couple lead remover chemical products that I tried.
wow....mine shoots in the same hole in semi at 10 yards....might look into replacing a barrel...ive never seen anything so far off.....what does the inside of the barrel look like?
How does the crown look?
Possibly damaged, dented?
It's possible, but not really likely, that the comp is actually squeezing the muzzle enough to cause bullet deformation.
Have you checked to make sure bullets aren't striking comp?