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 7.62×54mmR cartridge.
[5] Soviet sources indicate that the SN machine gun was installed in the wings of three Polikarpov I-16 aircraft in January 1939; these planes were given the designation I-16 Type 19 and they took part in the Winter War.
Although four planes were built in this configuration, they did not go into service; the Type 20 designation was then reused for I-16 aircraft only armed with ShKAS guns, but capable of carrying drop tanks.
[1] As with the UltraShKAS, the reliability of the SN machine gun was low, so it did not go into mass production.