This is the RPB Industries M10 Mac 10 in 45 acp, Open Bolt MAC-10 / 45 (Military Armament Corp. (M-10) The M-10 is a compact blowback operated machine pistol that was developed by Gordon Ingram in 1964. it is Chambered in 45 acp. RPB Industries manufactured the only semi open bolt variety for the M10 ever made, most were stamped "sM10" but a very few were made with the model stamped as "sapM10" (an abbreviation for semi auto pistol) This one is marked with the desired sapM10 rare stamp. This pistol is a pre-ban hard to find rare open bolt RPB industries in 45 acp. (there are multiple in 9MM) Has the barrel extender with heat shield making this pistol balance and easier to fire. Has a polymer grip attached to the back of the magwell. Comes with an extra bolt ($350 value) and 12 mags (these are upward of $100 each), extra buffer washer, case and original logo stamped loader. Great for the collector or shooter. Don't miss out on this one!