The M1903’s bolt combined features of the 98 Mauser--dual front locking lugs; rear safety lug; wing-type safety; and full-length, nonrotating extractor--with the knurled cocking piece and two-part striker of the Krag-Jorgensen.

The new cartridge’s potential was realized thanks in great part to the complex M1905 rear sight. It had a U-notch battle sight that was fixed for 545 yards and a fold-up leaf with a U-notch and two different apertures that were finely adjustable from 200 to 2,800 yards and for windage. By February 1907, all existing rifles had been upgraded, and new production began again. By 1912, all Army and Marine Corps units had received the M1903.

When the United States entered World War I, there were 843,239 M1903 rifles on hand. With the expansion of the armed forces, demand for rifles exceeded the facilities at both government arsenals. The decision was made to modify the P14 Enfield rifle, then being produced by Remington and Winchester, to accept the .30-06 cartridge, and production of the U.S. Magazine Rifle, Caliber .30, M1917 began. The M1917 proved easier to manufacture, and 2,200,000 were produced by 1918. During this same period, Springfield and Rock Island arsenals produced just 312,800 M1903 rifles.

During the war, some 65,000 M1903 rifles were modified to use the Pedersen Device. This unit temporarily replaced the bolt and turned the M1903 into a semiautomatic rifle that fired a .30-caliber pistol-type cartridge. A small, oval ejection port was milled into the left receiver wall, and a side-mounted 40-shot box magazine was fitted. The war ended before any of these devices were used in combat, and most were destroyed after the war.

Until late 1917, all M1903 receivers and bolts were casehardened, which proved insufficiently strong, especially with some of the haphazardly produced ammunition supplied by wartime contractors. In 1918, Springfield developed a double-heat-treating process that produced a stronger receiver. Rock Island began using nickel steel for receivers, something not done at Springfield until 1927.

These early M1903s, or “low numbered” rifles as they are known (#800,000 or lower for Springfield-made rifles and lower than #285,507 for the Rock Island rifles), were not withdrawn from the hands of troops already using them, but those in storage were declared war-reserve material and put aside.

M1903 production ended at Rock Island in June 1919, and only small numbers were produced at Springfield until 1927. On Jan. 9, 1936, the U.S. Army adopted the M1 Garand semiauto rifle, but teething problems with the Garand caused general issue to be postponed several times. When the U.S. became involved in World War II, the M1903 rifle was still standard issue for most Army units and the entire USMC. To make up for the shortfall in M1 production, the arsenal at Raritan, New Jersey, assembled M1903s from pre-war Springfield-made receivers with barrels and parts supplied by subcontractors.

In 1941, Remington leased the machinery at Rock Island Arsenal to produce M1903 rifles for an anticipated contract from Great Britain, but few were delivered due to U.S. entry into World War II. To reduce the time and cost of manufacture, parts such as the floorplate, trigger guard, and bands were constructed from stamped steel. Enough changes were made that these rifles were reclassified as the Model of 1903 (Modified) to distinguish them from earlier rifles.

It was necessary to issue several M1903 rifles to each U.S. Army unit for launching rifle grenades, as a suitable launcher was not available for the M1 rifle until late in 1943. Many M1903 rifles were also supplied to allied forces, especially the Free French and Nationalist Chinese.