9x39mm

The 9x39mm is a 7.62x39mm case necked up to take a nine-millimetre bullet, worked out in the Soviet Union in the first half of the 1980s by a team of four designers, N. V. Zabelin, L. S. Dvoryaninova, Y. Z. Frolov and E. S. Kornilova. It exists for one reason: it was designed from the start never to break the sound barrier, so that a suppressed weapon firing it makes no ballistic crack at all.

The dimensions say how narrow the brief was. Case length and overall length are 38.7 mm and 56.0 mm, the parent round’s figures to the hundredth of a millimetre, so the cartridge occupies the same magazine length and can be built on the same case-forming machinery. The head is unchanged at 11.35 mm. The neck goes from 8.6 mm to 9.72 mm and the bullet from 7.92 mm to 9.27 mm, and that is the whole of the modification.

Necking up is what makes subsonic work. A rifle case running a much wider, much heavier bullet at about 290 m/s is operating far below the pressure the case could take — C.I.P. still rates it at 3550 bar, the same as the 7.62x39mm — but it puts a 16-gram projectile into the air, roughly twice the mass a 7.62x39mm carries, which is where the energy comes back. The bullet is correspondingly short and blunt, and its aerodynamic penalty does not matter at the two to three hundred metres these weapons are sighted for. Two service loads share the case: the SP-5 with a conventional core and the hard-cored SP-6, marked with a blue tip, at almost the same mass and almost the same speed.

It has never had a civilian life to speak of. Almost every arm chambered for it is a Russian special-purpose weapon, and one commercial load appears in the record beside the two military ones.

Gaps on this page: no introduction year is recorded, because no free source gives one — the encyclopedia says only that the design was “finished in the mid 1980s”, and the arms built around it entered service in 1987. No ballistic coefficient is published for any of the three loads. All three velocities are the encyclopedia’s own table, which states a 10.5-inch test barrel for every row and cites the C.I.P. list rather than a manufacturer.