The SN (Savin and Norov) was an aircraft machine gun manufactured in small numbers in the Soviet Union before World War II. The gun was intended to achieve a higher rate of fire than the ShKAS, while using the same 7.62x54mmR cartridge. In order to achieve this goal, the primers were ignited while the barrel and bolt were moving in opposite directions. Source vary as to high a rate of fire was actually achieved. One indicates "more than 3600 RPM" while others give the 2800-3000 RPM range. An SN exemplar could be seen (in 1996) at the Central Air Force Museum.