Jhrulith and
Reod Dai seem to have misunderstood the meaning of the word
caliber.
7.62 mm is the diameter between the
grooves in a rifle barrel. So, the caliber of two very different cartridges --
7.62 x 51 mm NATO and
.300 Winchester Magnum is the same: 7.62 mm, but the latter cartridge has a much larger
muzzle velocity and
kinetic energy.
Other cartridges of the 7.62 mm / 0.3 inch caliber family are