5.45×18mm

The 5.45×18mm, given the GRAU index 7N7 in its standard ball loading, is a Soviet pistol cartridge a team at TsNIITochMash — Denisova, Bochin, Nikolayeva and Shamina — designed between 1969 and 1970 specifically around a new compact sidearm rather than the other way round. Its case is small and narrow, closer in scale to a rimfire round than to a typical centrefire pistol cartridge, chosen because the pistol itself was meant to be flat and pocketable enough for plainclothes and KGB carry.

It entered service in 1973 with the PSM (Pistolet Samozaryadny Malogabaritny, “self-loading compact pistol”), a slim blowback design whose slide and frame were shaped specifically to conceal well under clothing — the cartridge and the gun were developed as a single package rather than a round chosen for an existing pistol. Soviet and later Russian police, KGB and military personnel carried it as a discreet backup and concealed-carry sidearm through the late Soviet period and beyond.

Every dimension in this entry comes from the C.I.P. datasheet for “5,45 x 18”. Wikipedia’s infobox attributes its one recorded load’s bullet mass, 84mm test barrel and 320 m/s velocity to “C.I.P.” without a locatable clickable page for the ballistics figures specifically, so all three are recorded as estimated; ½mv² from the stated velocity and mass reproduces 153.6 J, not the infobox’s own published 128 J figure, an internal inconsistency in the source that is noted here rather than resolved by discarding one of the published numbers. No ballistic coefficient is published for this cartridge.