Post WW II the armed forces under NATO initially adopted the "battle rifle" concept - full size rifles capable of single shot or automatic fire. To go with this concept NATO retained a 'large' caliber bullet at 7.62mm (equivalent to .308 Winchester) called the 7.62x51 NATO to distinguish it from non-NATO 7.62mm bullets.

The actual difficulties of using this caliber (weight of ammunition and weapon as well as the difficultly of controlling the weapon on full auto) and the analyses from actual combat (especially Vietnam) lead to the dropping of this calibre and the acceptance of the American 5.56mm caliber. The old caliber is still in use within NATO for sniper weapons and more widely in non-NATO weapons such as the Kalashnikov AK-47.

The 7.62mm calibre is very powerful, able to penetrate six inches in 'soft' targets with around twice the lethal range of the 5.56mm. Although this brute speed means it can actually cause less damage than the 5.56mm as the bullet passes straight through the body rather than expending its energy within the target.