Well, not an expert, but have you got any information here? The technology was pretty mature in 1921, there were a few rounds of refinement before that. Machin

Well, not an expert, but have you got any information here? The technology was pretty mature in 1921, there were a few rounds of refinement before that. Machinists definitely talked about "one thou" back then. The same M2s which fire these things have been in production for over 80 years. I'm sure there have been small tweaks, special versions, etc, but basic compatibility has remained.