What caliber rifle is a AK-47?
The round fired in an AK 47 is a 7.62x39. This number denotes
the bullet diameter, 7.62mm and the length of the cartridge (the
brass) which is 39mm. Now, the 7.62 bullet diameter is a .30
caliber in western measurements. Specifically, nearly identical to
a .308.
Here, we get into some common misconceptions. To begin, though
the 7.62mm bullet is virtually identical to a .308 bullet, but the
39mm case/cartridge/brass is significantly shorter than a .308
winchester. The .308 Winchester is the caliber of the standard
sniper rifle used by the US military. This .308 is virtually
identical to the NATO 7.62 x 51. Same bullet diameter but with a
longer cartridge/brass. I say the .308 is 'virtually' identical
because a NATO 7.62x51 can be fired by a rifle chambered for .308
Winchester but one should not fire a .308 win from a rifle
chambered for the 7.62x51. This is because the chamber pressures
are measured differently.
RELOADING NOTE-one can NOT reload a 7.62 x 51 NATO cartridge
using the same reloading data as would be used for a .308
Winchester! The 7.62 x 51 NATO brass is thicker than the .308 Win
so to load with the same number of grains/weight of powder would
produce dangerously high chamber pressures which would result in,
at best, innacurate rounds and, most probably, rounds that will
cause the rifle to fail/blow up in your face. Chamber pressure in
NATO rounds are measured in CUP (Copper Units of Pressure) and NOT
psi. See: http://en.wikipedia.org/wiki/Copper_units_of_pressure
TO SEE IF YOU ARE LOADING A NATO CARTRIDGE LOOK FOR THE "PLUS"
SIGN HEADSTAMP: http://www.frfrogspad.com/natocase.jpg there is a
'plus' sign or cross in a circle. A cartridge with this stamp is
NOT THE SAME as a .308 win cartridge.
Hope this helped!