the magazines on EM2s), included the Universal Optical Sight (unit sight) due to the inability to add more traditional sights onto the rifle, had a carrying handle built into the top, could fire semi-automatic or fully automatic and the .280 (7 mm) round was accurate to about . The two designs were superficially similar but were internally very different in design and construction, with no parts in common other than sights. The EM-1 used thick steel plate pressings for simpler manufacture, a roller locked short recoil mechanism, and was somewhat heavier at about with an empty magazine. With uncommon flapper locking and a gas piston above the barrel, EM-2 was similar to Gewehr 43 in its mechanics, although it used a long stroke instead of a short stroke. A fifth design was commissioned from the BSA company, who built prototypes of a more conventional rifle using the same round, the BSA 28P. The EM-2 was eventually selected as the better design, and was adopted as the British Army's new rifle on 25 April 1951 as the Rifle, Automatic, Calibre .280, Number 9, the designation by which it had been known in the War Office since the American weapons tests of 1950. In common with other 20th century British designs such as the P14 and SA80, the EM-2 was designed to achieve a high degree of accuracy due to the tradition of British Army emphasis on marksmanship. NATO standardisation With the creation of NATO in 1949, there was a clear preference that NATO forces would have commonality of weapons and ammunition, so weapons designs had to meet with the approval of more than one government, and it was hoped, would be adopted by the organisation as a whole. It was at this point that the US put forth its own designs for NATO standardisation, using the 7.62×51mm NATO round in their prototype T25 and T44 rifles. Matters came to a head in 1951 in a shoot-off conducted at the Aberdeen Proving Grounds, with the US claiming the British round was underpowered, and the British claiming the US round was too powerful to be used in a rifle in full-automatic mode. At the same trials the Belgian .280 FN FAL was also tested. A series of lengthy debates followed, which were finally settled in an unlikely fashion when Canada stated they would use the British .280 round, but only if the US