History of Headspacing
“‘Faith’ that does not survive collision with truth is not worth regretting”
Arthur C Clark
“Semi-rimmed” cartridges (25ACP, 32 ACP, 38ACP, 9×20 or “9mm Browning,” 6.5×50 Arisaka, 444 Marlin) enjoyed only a brief period of popularity during the first half of the 1900s. They combined the (mostly) positive head-spacing of a rim, with the ability to be used in a box magazine without the problem of rim-lock.
Semi-rimmed cartridges came about when box magazines became popular, but industrial cartridge manufacturing was incapable of dimensioning precise enough to use the cartridge shoulder or case mouth for consistent head-spacing.
During the 1900s, Russians in particular lacked the industrial precision to manufacture military ammunition with shoulder dimensions consistent enough to insure positive head-spacing, so they stuck-with the 7.62x54R (the “R” if for “rimmed”) cartridge (today confined to machineguns).
With rimmed (or ‘flanged”) cartridges, shoulder dimensions are basically irrelevant!
However, manufacturing methods quickly evolved (at least in the West) sufficiently to overcome that limitation, making semi-rimmed cartridges obsolete, which they mostly are today.
“Today’s ‘emerging technology’ is tomorrow’s museum exhibit!”
Anon
/John
