.30 caliber rimless bottleneck rifle cartridge (Winchester)

.308 is the (approximate) diameter of the rifle bore for the caliber cited (in inches).

The .308 Winchester is the civilian precursor to the 7.62x51mm NATO cartridge that replaced .30-06. It uses the same basic projectiles as the .30-06; however the .308 Winchester case is shorter than the .30-06 case to fit into short action rifles. In order to maintain similar ballistics with the .30-06, the diameter of the .308 case is increased to make for a similar volume for the powder charge.

Ballistics of the .308 are very similar to the .30-06. The dimensions of the .308 are virtually identical to the 7.62x51mm cartridge, however due to differences in pressures and dimensions of the chambers, they are not strictly interchangeable. Generally speaking it is safe to shoot 7.62x51mm cartridges from a .308 chamber, however the reverse may not be true. In keeping with the “better safe than sorry” maxim, civilian .308 Winchester ammunition should not be used in a 7.62x51mm rifle.