The Nikitin-Sokolov PN1, also known as the TKB-521, is a prototype general purpose machine gun.
The PN1 was designed by two designers, Grigory Nikitin and Yuri Sokolov and passed field tests in 1958. It was to be the standard-issue general purpose machine gun for the Soviet military. All was going well for the PN1 until a group of designers from IZHMEKH and submitted their machine gun design; the IZHMEKH design won out as it was said that it was cheaper and more reliable than the Nikitin-Sokolov design, and the PN1 faded into history. Nikitin, Sokolov and V. I. Volkov would later work together to produce the very successful NSV machine gun.
The PN1 is gas-operated with a rotating bolt. The weapon feeds from the right, as with most Russian machine guns of the time.