No P-14's were "converted" to use the U.S. Army Ordnance contracted with the same companies to modify the P-14 to use the U.S.30-'06 ammunition that rifle was the U.S. entered the war, with a severe shortage of M1903 rifles. Just about the time the British contracts were completed, the U.S. The three factories, at Ilion, NY, New Haven, CT, and Eddystone, PA, produced a total of 1,117,850 P-14 rifles. But they contracted to three American companies, Remington, Winchester, and a new entity, associated with Remington, to make the new rifle for them. When war came, the British decided not to produce any more P-14's, and devote their factories to production of the SMLE. 276 Enfield is a very fat cartridge, over 1/2 inch at the base, with a rebated rim, so the magazine could be used with the rimmed. The change was made easier by the fact that the. 303 cartridge, calling the rifle the Pattern 1914 or P-14. As war approached, the British decided that it was not a good time to change ammunition, but they still wanted to keep the new rifle, so they dropped P-13 development after a few thousand had been made and modified the design to use the standard. In any case, the result was called the Pattern 1913, or P-13. 276 Enfield was intended to match the ballistics of the Ross cartridge, which was the darling of the high-velocity crowd at that time. 280 Ross they are very different cartridges, though the. They chambered it for a new cartridge, the. M1903 Springfield, with some additions to suit their own needs. The British decided well before WWI that the Mk III SMLE was outdated and they needed a more modern rifle, and designed one based on a combination of the Mauser 1898 and the U.S.