They are cool from a small arms developmental perspective. Way over-engineered for the relatively low-powered cartridge that it fired, however sheet-metal pressing for firearms manufacture was in its infancy and better safe than sorry when it came to the overly-thick gauge of steel used in the Receiver stampings. That is why it is a 13 lb "monster" to carry and (occasionally) shoulder. A dream to fire however, especially in full-auto where it just sort of sits there with a gentle rearwards pressure. Not jarring recoil at all like an AKM, as the Stg44 receiver was long enough to permit Bolt-Carrier run-out under the Operating Spring's tension. So it just chugs away at a relatively sedate 600-ish rds/minute, easily putting 'em where it counts without drama out to 300m. Precisely as it was designed to do. Not bad for 1943 tech. The developmental race between the various wartime German manufacturers is in and of itself, an interesting read. The fact that they kept it a secret from the big cheese by calling it an SMG (MP-43/MP-44, with "MP" standing for Machine Pistol in German) is also interesting. The entire competitive development and testing process occurred right under the little moustache's nose, so to speak. They are a highly interesting footnote in history, although had the Americans given the M1 Carbine a Selector Switch prior to 1944 they would have been the first to issue an "Assault Rifle" by today's accepted definition of a shoulder-weapon firing an intermediate rifle/carbine cartridge with controllable, full-automatic capability.
The U.S. actually beat the Germans to the punch when it came to recognizing the need for an intermediate cartridge to bridge the pistol/rifle ammo gap that the SMG could not fill due to range limitations. The M1 Carbine was fielded in mid-1942, just as the Germans were getting down to detailed development of a similar weapon, although based on a different employment concept. Whereas the Americans saw the M1 Carbine as a stop-gap weapon for second-echelon support troops and F-echelon soldiers manning leadership positions or crew-served weapon systems, the Germans were looking for a widespread replacement for the bolt-action Mauser firing its overly-powerful 7.92mm full-sized round (aka: 8mm Mauser). The Germans intended to field entire units equipped with the MP-43/44/Stg-44, with the MP40 reserved for Crew-Served Weapon and Rear Echelon personnel. They were the first to recognize that the intermediate cartridge would permit controllable automatic fire in a select-fire carbine for general infantry use. The US did not figure that out with the M2 Carbine until experience was gained fighting in the Pacific jungles during the latter stages of WW2. The M2 Carbine did not see widespread issue until the Korean War kicked off in the summer of 1950 and still, the Americans did not really learn their lesson regarding the wisdom of using a true intermediate cartridge until the Vietnam War and the advent of the 5.56mm cartridge in the mid 1960s. The Russians figured it out in 1944/45 when they started capturing the Stg-44 in increasing numbers. They developed and kept the 7.62x39mm humming along uninterrupted until the 5.45mm cartridge was developed in the late 1970s/early 1980s. Not stupid, those Russians....but then neither were the Germans. We were kind of slow learners though....
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