The 9×39mm is a Soviet / Russian rifle cartridge.
It is based on the Russian 7.62×39 mm round, but with an expanded neck to accommodate a 9 mm (.356 caliber) bullet. The cartridge was designed by N. Zabelin, L. Dvoryaninova and Y. Frolov of the TsNIITochMash in the 1980s. The intent was to create a subsonic cartridge for suppressed firearms for special forces units that had more power, range and penetration than handgun cartridges. The 5.45×39 mm cartridge introduced in 1974 for the AK-74 lacks sufficient bullet weight (at 53 gr to 80 gr) for acceptable energy at subsonic velocities. The bullet of the 9×39 mm is approximately 16 g (250 gr), double that of the normal 123 gr 7.62×39 mm round, and is subsonic. This slow velocity does not produce a sonic boom, but does limit the muzzle energy and effective range of a weapon when compared to non-suppressed rifles. The round has an effective lethal range of 300 to 400 meters and a maximum penetration of up to 8 mm of steel. Like the 5.45×39mm cartridge, 9×39mm SP-5 features an airpocket in the tip, which improves its capability to yaw after impact, and thus its effect in soft tissue.