There were many difficulties during the initial phase of production. The first production models had stamped sheet metal receivers. Difficulties were encountered in welding the guide and ejector rails, causing high rejection rates.[16] Instead of halting production, a heavy machined receiver was substituted for the sheet metal receiver.[17] This was a more costly process, but the use of machined receivers accelerated production as tooling and labor for the earlier Mosin-Nagant rifle's machined receiver were easily adapted. Partly because of these problems, the Soviets were not able to distribute large numbers of the new rifle to soldiers until 1956. During this time, production of the interim SKS rifle continued.[17]
Once manufacturing difficulties had been overcome, a redesigned version designated the AKM (M for "modernized" or "upgraded" — in Russian: (Автомат Калашникова Модернизированный [Avtomat Kalashnikova Modernizirovanniy]) was introduced in 1959.[18] This new model used a stamped sheet metal receiver