Firing Pin, recoil spring assembly, Serial number 9184k. German MP 40/I submachine gun Serial number 9184 k (no magazine) DEACTIVATED Believed to be the one donated by John Duncan Manson. The MP 40 was a (32 round) magazine fed which worked on a straight blowback and open bolt to fire. MP 40 — main production version MP 40/I — experiment with two side by side 32-round magazines, sometimes (incorrectly) called MP 40/II.The MP 40/I was tested in 1942. This version of the MP 40 has a two-magazine receiver that slides horizontally to use the additional magazine when the first becomes depleted. This design was intended to counter the superior firepower of the Soviet PPSh-41, but made the weapon heavy and unbalanced in the field, and did not work well. However, by 1943 the Soviets shifted the production of PPSh-41 drums to 35 round magazines due to combat malfunctions. In 2001, only five genuine exemplars of the MP40/I were known to exist. The dual feed system is a feature shared with another rare weapon, the EMP 44. NOTES (WIKIPEDIA):