>>27709467This is not strictly true. Lower velocity pistol cartridges, such as .45acp, do not gain much from a longer rifle length barrel. High pressure, high velocity pistol cartridges DO gain added performance.
9mm is a perfect example. 9mm can gain as much as 600fps out of a rifle length barrel.
An extreme example would be the Magnum calibers. Out of an 18 inch rifle, .357 Magnum's muzzle energy is equal to intermediate calibers like .5.56 NATO and .44 Magnum is equal to battle rifle calibers at the muzzle.
These cartridges are limited by their bullet shapes and energy falls off rapidly much past 200 yards, but within 200 yards high velocity pistol cartridges can hit hard from a rifle barrel.
