Developed and patented by James M. Leatherwood, the Adjustable Ranging Telescope (ART) system combines a range-finding scale inside of a

telescopic sight A telescopic sight, commonly called a scope informally, is an optical sighting device based on a refracting telescope. It is equipped with some form of a referencing pattern – known as a ''reticle'' – mounted in a focally appropriate po ...

(scope) with an adjustable

cam Calmodulin (CaM) (an abbreviation for calcium-modulated protein) is a multifunctional intermediate calcium-binding messenger protein expressed in all eukaryotic cells. It is an intracellular target of the secondary messenger Ca2+, and the bin ...

integrated into the scope's mount. This raises or lowers the rear of the sight to compensate for the ballistic rise or fall of the projectile. The cam is preset for a specific cartridge, i.e., the 7.62 mm NATO round. Due to the fact that the range cam is locked to the magnification ring, the range is automatically set, and the ballistic fall of the shot is accounted for. This then allows the shooter to place the optic's aiming point directly on the target. During the

Vietnam War The Vietnam War (also known by #Names, other names) was a conflict in Vietnam, Laos, and Cambodia from 1 November 1955 to the fall of Saigon on 30 April 1975. It was the second of the Indochina Wars and was officially fought between North Vie ...

Lieutenant A lieutenant ( , ; abbreviated Lt., Lt, LT, Lieut and similar) is a commissioned officer rank in the armed forces of many nations. The meaning of lieutenant differs in different militaries (see comparative military ranks), but it is often sub ...

Leatherwood, who already had the patents for his ART system, entered the Army and began working with U.S. Army Ordnance specialists. The combination of the Leatherwood Adjustable Ranging Telescope (ART) with M14 National Match rifles went on to create the M21 Sniper Rifle.

References

Firearm sights {{optics-stub