The M1903A4 was the U.S. Army's sniper rifle of choice during the Second World War. The M1903A4 was a variation of the M1903A3. The only difference between receivers was that the model and serial number on the receiver were split on 1903A4 to make room for the Redfield scope mount. The Redfield scope mount removed the rear peep sight that was standard on the M1903A3. The scope used on the M1903A4 was a Weaver Model 330 or 330C, which was a 2.75x telescopic sight. The receivers were tested by Remington Arms and those that were deemed best, meaning those closest to design specifications were selected to become M1903A4's. The barrels were also selected specifically to be added to the M1903A4 rifle only if they were within almost exact specifications for the design. The front sight on the barrel was never installed on the A4 barrels, however, the notch for it was still in place. Barrel specifications were, in general, unchanged between the M1903A3 and M1903A4, however, the War Department did start installing barrels with 2 groove rifling instead of 4 groove, despite the lack of clear changes from the 4 groove rifling that was the standard up until 1942.
By some accounts, the M1903A4 was inadequate as a sniper rifle. The M1903A4 was a relatively accurate rifle with an effective range of about 600 yards (550m). These limitations on long-range targeting were due to the limited field of view present in both the M73 and M73B1 scopes. From its adoption in 1943 until the end of the war it was used extensively in every theater of operation by both the US Army and the USMC. The Weaver scopes (later standardized as the M73 and M73B1) were not only low-powered in magnification, they were not waterproofed, and frequently fogged over or became waterlogged during humidity changes. In addition, the M81/82 optional scopes also had significant flaws. They most notably had less power (2.2x vs. 2.75x) and, like the other scopes on the M1903A4, had serious issues with the field of view. The USMC would eventually switch to a large 8x scope that spanned the length of the rifle designed by John Unertl.