>>63831380
They might have sleeved it, .45 caliber would give you a lot of room inside to work with. It seems like it's probably a later conversion of an original Chinese .45 Thompson clone, compare to how the Chinese Communists would caliber convert some captured 9mm Sten guns to 7.62mm (in which case they tended to give those guns longer barrels).
The 7.62mm Sten guns would use modified PPS-43 magazines, the magazine on that Thompson is a PPS-43 magazine as well, but I don't know if it's modified. The Thompson's wide (front to back) magwell seems like it'd accommodate the new magwell insert pretty well.
Supposedly, the converted 7.62mm Sten guns functioned pretty poorly and in hindsight it was looked at as a bad idea, who knows how well these Thompsons worked. The 1921 Thompson would have still used the Blish Lock, and I wonder if that, A, was copied by whichever actual Chinese arsenal built the clone to begin with, and B, if that was then still kept when this gun was later worked over by the Communists. The best thing to do would be to simplify the bolt into a blowback lump when you were already working these over.
Pic related is another 7.62mm Thompson, this one is built on an American M1A1, so it would already be a blowback gun. .45 isn't as zippy as 7.62mm, but instead it's really heavy, so I wonder how well the .45 bolt and recoil spring would translate for 7.62mm
