The Mosin-Nagant M1891 Avtomat is a heavily modified fully automatic Russian service rifle with an increased internal magazine. Note: While the game calls this a Mosin Nagant Avtomat, it is in fact a Huot automatic rifle - a WW1 era modification of the Canadian Ross rifle.
The two most successful modern assault rifles are the AK-47 and the M16 designs and their derivatives. The StG 44 was adopted by the Wehrmacht in 1944. It fires the 7.9233mm Kurz round.