The Maschinenkarabiner 1942, more commonly known as the MKb 42 (or MkB 42), is a prototype assault rifle design.
Contracts for a rifle firing 7.92×33mm rounds were sent to both Haenel and Walther, who then cobbled up a design based on the given specifications. A prototype rifle that was made by both Haenel and Walther was tested at Kummersdorf in December 1940 by the HWA; it performed poorly, in which it jammed up multiple times, several barrels bulged and one barrel had a catastrophic failure. The poor performance was blamed on low quality ammunition.
Haenel later submitted a second prototype for their MKb 42 design, the MKb 42(H), and it was later tested on July 9, 1942. However, it still had faults; despite 3654 shots being fired, 11 cases separated, 67 were duds (though 56 fired on the second trial), with numerous others stovepipe jamming. Failures for this design were blamed on it being a prototype design. The MKb 42(H) was later tested against the newly designed Walther weapon, designated the MKb 42(W) in the front lines, with the Haenel being chosen due to better reliability and overall performance. Despite the MKb 42(W) showing better single-shot accuracy than the MKb 42(H), it was ultimately rejected due to its questionable action; no further action was taken to improve the weapon's design as Walther was already having their hands full with delivering their P38 pistol to the German army. In light of this, the German army requested Haenel to make another variant of their MKb 42(H), with minor changes.
The MKb 42(H) saw service in 1942 and 1943, but as work progressed, Hitler suspended all rifle programs due to infighting within the Third Reich, and recommended that newer submachine guns were to be built. With that, he also strongly discouraged the use of the 7.92x33mm Kurz cartridge. In order to keep the MKb 42(H) alive, Haenel renamed the weapon the MP 43. Haenel later tried to make the MP 43 a replacement for the K98k, but much time was wasted and many faults were discovered, such as the cartridge fired by the MP 43 being too weak to fire rifle grenades, among other reasons.
As such, the MP 43 was relegated from being a replacement for the K98k, to becoming a weapon to supplement the K98k. Due to this, a few changes had to be made to the MP 43, such as the removal of the bayonet lug and other things. However, Adolf Hitler noticed this deception and halted the program, but allowed it to recommence in March 1943 for evaluation purposes. Evaluation lasted for six months, with results from tests being positive; Hitler allowed the program to fully recommence in order to make mass-production of the MP 43 possible at a time of crisis, with production continuing and distribution to different units proceeding.
In April 1944, Hitler took some interest to tests the weapons were undergoing, and ordered the weapon to be renamed the MP 44, along with some minor updates to its design. In July 1944, at a meeting of various army heads the Eastern Front, Hitler asked a general as to what they needed, to which the general exclaimed: "More of these new rifles!", causing some confusion, with Hitler reportedly asking: "What new rifle?". After Hitler saw the MP 44 being demonstrated, he was impressed, and gave the weapon the title of Sturmgewehr. Seeing the possibility of mass propaganda, he renamed the weapon again to Sturmgewehr 44, to show other powers the new class of weapons it represented. From there, the term "assault rifle" was born, and the MP 44 became the StG 44.
The MKb 42(H) fired from a tilting open bolt and was striker-fired, while the MKb 42(W) fired from a rotating closed bolt and was hammer-fired; however, the MKb 42(H) was later modified to fire from a closed bolt and be hammer-fired.
The MKb 42(H) uses a long-stroke gas piston located above the barrel. The barrel locking of the MKb 42(H) was achieved by tipping the rear part of the bolt down into the locking recess, cut in the machined steel insert in the receiver.
The MKb 42(W) was based on one of Walther's earlier prototype rifles, the A115, and had a rather odd gas system, with an annular gas piston located around the barrel. The MKb 42(W)'s bolt has 2 locking lugs and is of a somewhat complicated design.
The MKb 42(H) was made out of stamped steel to take advantage of the maximum usage of stamping and welding needed, and because of that, Merz Worke, a company with no prior knowledge in firearms design, but a force in the stamping and welding industries, joined Haenel for the design of the MKb 42(H). The MKb 42(W) was also made out of stamped steel.
- Original 1940 prototype
The original prototype submitted by both Haenel and Walther.
- MKb 42(H)
The Haenel design. It had a long-stroke gas piston system and fired from an open bolt, though later it was modified to fire from a closed bolt. This design eventually became the basis of what would be the StG 44.
- MKb 42(W)
The Walther design. It had an odd annular gas piston with a complex rotating bolt with two locking lugs. This design was rejected despite showing some promise, with only roughly 200 made, but the MKb 42(W) was recommended to fire from a closed bolt and hammer-fired just like Walther's design.
- In 2017, an exploded view image of an MKb 42(H) was depicted on new sculpture dedicated to Mikhail Kalashnikov in Moscow. The image is identical to schematics found on the web leading to the conclusion that the sculptors used web search for reference images. The MKb 42(H) image was later removed from the monument.