M21 7.62mm Sniper Weapon System
The National Match M14 rifle and its scope makeup the M21 sniper weapon system. The M21 is accurized IAW United States Army Marksmanship Training Unit specifications and has the same basic design and operation as the standard M14 rifle, except for specially selected and hand-fitted parts.
Auto-ranging telescopes are part of the M21 system. The 2 types of ARTs on the M21 system are the ART I and ART II. The basic design and operating principle of both scopes are the same. The ART has a commercially procured 3- to 9-variable-power telescopic scopesight, modified for use with the sniper rifle. This scope has a modified reticle with a ballistic earn mounted to the power adjustment ring on the ART I. The ART II has a separate ballistic cam and power ring. The ART is mounted on a spring-loaded base mount that is adapted to fit the M14.
The XM21 Sniper Rifle was developed jointly by the Army Weapons Command at Rock Island Arsenal, Illinois; Combat Development Command at Fort Benning, Georgia; and the Limited Warfare Agency, at Aberdeen Proving Ground, Maryland. The XM21 was an accurized M14 National Match semi-automatic rifle equipped with a Leatherwood 3x-9x Adjustable Ranging Telescope (ART). The Rock Island Arsenal converted 1,435 M14 National Match rifles to XM21 sniper rifles for initial fielding to Vietnam in 1969. The rifle was initially fielded with a hardwood stock, which was later replaced with a fiberglass stock.
The XM21 was officially type classified standard as the M21 in 1975, though it had been informally called the M21 since December 1969. It was the primary Army sniper rifle of the Vietnam war and remained standard until replaced by the bolt-action M24 Sniper Weapon System beginning in 1988. The M21 was accurate to 750 yards (690 meters). The rifle used US match grade M118 NATO 7.62mm cartridges, in 5-round or 20-round magazines. The ART telescope featured a variable magnification power of from 3x to 9x, for adjustable ranging between 300 and 900 meters. This adjustable ranging feature removed much of the guesswork from aiming at the target. The ART was ballistically matched with US M118 NATO ammunition.
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