This experimental Thompson submachine gun is kept and displayed in the Military Historical Museum of Artillery, Engineers and Signal Corps which is located in Saint Petersburg, Russia. The photos of this Model 1928A1 Thompson SMG were taken by a fellow firearms researcher Marin Milchev who kindly provided them to TFB to be used in this article.
The information about this gun virtually does not exist. Well, at least I couldn’t find anything. I asked many renown industry experts for help with the identification of the gun, but we couldn’t find any data about this experimental stock. The museum label is pretty much the only source which translates:
Submachine gun of Thompson system, model of 1928 A1, experimental version with a folding metal stock (M1928A1), USA.
Caliber 11.43mm, barrel length 319mm (with the muzzle brake), length with a folded/detached stock 645mm, length with the extended stock 879mm, magazine capacity 20 rounds.
As you can see, the label doesn’t really give any valuable information. It is unknown whether this was a US experiment and somehow appeared in the Soviet Union or was it a Soviet experiment? The Soviet Union received some Thompson submachine guns as part of the Lend-Lease program. Also, some Tommy guns were acquired earlier by Soviet special services (NKVD/OGPU) in Mexico.
According to Marin, this top folding stock looks to be a machined one. The butt portion of the stock has a U-shape which is designed to fit around the receiver when it is folded over the latter. In the image embedded below, you can see the wear marks on the receiver, (in front of the magazine well) which are most likely caused by the stock.
Below you can also find a set of images with close-up views on different parts of this gun.
If you know anything about this experimental Tommy gun, please share the information in the comments section.
Many thanks to Marin Milchev for the provided information!