The modularity and clever design of the Stemple Takedown Gun is perhaps best illustrated by the STG-M1A and STG-1928 (these are the same gun with either a horizontal or vertical front grip). In the early 2000s a bunch of Thompson parts kits came into the US, WW2 vintage lend-lease guns sent to Russia. They were M1 and M1A1 models, and had intact barrels but torch-cut receivers. BRP, who makes the Stemple, realized that the sear-to-magwell dimensions on the Thompson were almost identical to the Suomi and Stemple – and that he could make a version of the STG that was a nearly perfect clone of the M1 Thompson.
The registered Stemple receiver slides into a square Thompson lookalike housing, and original Thompson grips, stocks, and hand guards are used. It is chambered for .45ACP, using original Thompson stick magazines (naturally). The result isn a submachine gun that almost perfectly duplicates the handling of a true Thompson, without the historical value that makes the Thompson so expensive and keeps many owners from wanting to actually take their Thompsons out to the range.
Note that the example in this video is an early example, and models made today are able to take both stick and drum magazines. Also, due to the deign of the disconnector in the original Thompson FCG, the semiauto setting is not functional in the Stemple version – it’s only full automatic.