The hybrid of original Mauser C96 and the Mauser M712 Schnellfeuer is available in the game, referred to simply as "Mauser". The weapon lacks the M712's fire selector and shoots only with single shots, meaning that it is generally a C96 with the M712's detachable magazines. It is modelled with 10 rounds magazine, but holds only 9 rounds. Ammunition in the form of spare magazines can be found here and there in the game.
The Mosin Nagant M91/30 is one of the weapons available, including a usable bayonet. The game manual inexplicably describes this as a chambered for .375 round (a massive big game cartridge, that Mosin-Nagant understandably never used). Appears in both standard and sniper variants. Also carried in the game by undead soldiers (for whatever reason, wearing insanely outdated uniforms, canceled by the mid-1920s).
The Model 24 Stielhandgranate. For some reason, they are only used by enemies, and the player can only get them through console commands. The massive use of German grenades after the war is not entirely clear (and their fillings are known to be poorly shelf-stable); perhaps the developers confused them with the Soviet RGD-33.