https://www.starlinebrass.com/brass-cases/9X21-Brass/
if you use the shortest available bullets, like the 90 gr jhp's. The extra powder space lets a 3" barreled pocket 9mm get a hollowbased, 45 gr solid copper hp to 2200 fps, which is 500 ft lbs, just like a 4" 357 mag. Not bad in a 6" long, 15 oz gun that lies nice and flat in your pocket. The recoil is like that of a Makarov, very mild, too.
now watch some know nothing post about big, heavy bullets doing nothing more in 9x21 than in 9x19.
if you use the shortest available bullets, like the 90 gr jhp's. The extra powder space lets a 3" barreled pocket 9mm get a hollowbased, 45 gr solid copper hp to 2200 fps, which is 500 ft lbs, just like a 4" 357 mag. Not bad in a 6" long, 15 oz gun that lies nice and flat in your pocket. The recoil is like that of a Makarov, very mild, too.
now watch some know nothing post about big, heavy bullets doing nothing more in 9x21 than in 9x19.