7.62×38mmR

The 7.62×38mmR is the revolver cartridge Léon Nagant designed in 1895 for the Imperial Russian gas-seal revolver that carries his name, and it remained standard Russian and Soviet service ammunition into the Cold War. Its defining feature is not calibre or power but geometry: the bullet is seated entirely inside the case and the mouth is crimped shut over it, so the cartridge’s overall length is shorter than its own case length — a reader can see the case mouth closed over the bullet in a way no ordinary revolver round shows.

That shape exists for one mechanical reason. The Nagant M1895 revolver seals its cylinder-to-barrel gap by camming the cylinder forward on firing, and the case mouth rides into the forcing cone and expands to close the gap. A conventional cartridge with an exposed bullet nose cannot do that; the fully enclosed case mouth is what lets the cylinder gap seal at all, at the cost of a low-pressure, low-velocity round by the standards of its era.

This entry’s dimensions and maximum pressure come directly from the C.I.P.’s English-language TDCC datasheet for “7,62 Nagant”. The two load masses and velocities in the Wikipedia infobox carry no citation on Wikipedia itself and no test barrel is stated in a way that is verifiable independently of that infobox, so both loads are recorded here as estimated rather than verified; the ½mv² check does at least confirm the m/s and joule readings are self-consistent. No ballistic coefficient for either bullet was found.