[JJ_BPK]

After WW II, the Army ALMOST selected the FN FAL. The initial tests were with the British 280 cal. But Mother Army had to have a .30 inch, so the 7.62x51 was born :]

Originally Posted by .280 British - wikipedia

The .280 British was an experimental rimless bottlenecked intermediate rifle cartridge. It was later designated 7 mm MK1Z, and has also been known as 7 mm NATO, .280/30, .280 Enfield, .280 NATO, 7 mm FN Short, and 7×43mm.

Like most armed forces in the immediate post-World War II era, the British Army began experimenting with lighter rounds after meeting the German StG 44 in combat. The Army began development in the late 1940s, with subsequent help from Fabrique Nationale in Belgium and the Canadian Army. The .280 British was tested in a variety of rifles and machine guns including the EM-2, Lee–Enfield, FN FAL, Bren, M1 Garand and Taden gun.

Despite its success as an intermediate cartridge, the .280 British was not considered powerful enough by the U.S. Army and several variants of the .280 British were created in an attempt to appease the U.S. Army. However, the U.S. Army continued to reject these variants, ultimately adopting the 7.62×51mm NATO.