In about 1910, the British decided to change their service round from a rimmed cartridge to a rimless design, following the Mauser pattern. The new round would also be smaller, going from a .311 to a .276 diameter bullet. The Brits took the M98 Mauser design and modified it, coming up with the Pattern 1912 Enfield. Remington was awarded a contract to build a new factury in Eddystone, Pa. for the manufacture of these rifles. Remington assemblied about 1500 rifles in the new caliber before WWI broke out. The Brits then change the contract and Remington started building the rifles in, 303 British caliber.Remington also provided Winchester with tooling. These rifles were known as Pattern 1914 or P14, rifles. When the new designations came in in the 1930s, these rifles were re-designated as No. 3 rifles.This is why the rifle is sometimes known as "the American Enfield".
To change to the American service round, the Cartridge, Caliber .30, Model of 1906 (.30/06), the barrel and bolt face were redesgined. The magizine will hold 6 rounds of .30/06, as it was designed to accomidate 5 rounds of the rimmed .303 British cartridges. This gives the rifle that "Pregant" appearance.
The "U.S. Rifle, Caliber .30, Model of 1917" was a bolt action rifle produced between 1917 and 1920, adopted by the US Army ,due to the Springfield and Rock Island arsenals' inability to increase production of the Springfield Model 1903 prior to World War I. The caliber was changed from the .303 to .30-06 when it was adopted by the US Army. After World War I, the M1917s were put into storage while the more popular and on-the-rise M-1903s remained the standard service rifle for the US Army.
Early into World War II - being desperate for rifles - the British accepted many of the United States' M-1917s via the Lend-Lease Program. When given to the British, the guns had to be clearly marked as using the non-standard .303 ammunition; with a large red stripe around the guns' handguards in order to avoid mistakes.
In 1919, Remington brought out a factury spotrizied model, using surplus G.I. parts on new recirvers. This was the Model 40. Until the mid-1920s, .30/06 was the only cartridge that the rifle came in.