Reference questions from my post above. For kwill1911, the OSI M-36s were marked "OSI" on the frame just above the trigger guard. I don't recall which side but IIRC they were marked on both sides. Not sure if they were electro pencil or stamped, they looked stamped to me. The 36 in my thumbnail is not an OSI gun, it is one of mine set up like the OSI 36.
For ordnanceguy, check Post #8 by oldtanker above for a pic of the ammo box and a PGU-12/B round; however, the headstamp is not clear in the pic.

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