In the late 1960s, a rising level of secrecy in the Soviet Union brought forward the need for a compact, suppressed, semi-automatic pistol to fill the role of a KGB operative sidearm. The Makarov, while largely sufficient, needed many adjustments to accept a detachable suppressor. The PB (Pistolet Besshumnyy) was designed, using the Makarov PM as it's base design. Half of the barrel functions as the basis for an integral suppressor, while the second half is detachable to allow for the pistol to be carried discretely.
In game, you can expect the PB to function as a concealable pistol with adequate damage, as well as having an attachable suppressor that does not lower damage. It has a few available modifications, mostly in the form of different grip sets.