.30 carbine have had almost the same case capacity as the 7.5 FK cartridge (1.4 ccm vs. 1.5ccm). Barrel was longer at the M1 Carbine, making the heavier bullet go as fast as that of the 7.5 FK, for extra muzzle energy.
The .30 Carbine and it's round did their job well, my personal favorite ww2...