The SCAR series of rifles were manufactured to satisfy the requirements for the SCAR competition held by the United States Special Operations Command (USSOCOM). The first rifles were issued in April 2009.
The SCAR is a modular, compact, lightweight, select-fire rifle. The lower receiver is made of polymer; the SCAR's pistol grip is similar to the standard pistol grip on an AR-15. The upper receiver assembly has an integral rail on top that extends to the gas block, and is made of extruded aluminum. The barrel can be easily changed, and several barrel lengths are used: 13-inch for CQC (close quarters combat), the standard 16-inch barrel, and a 20-inch barrel. The SCAR rifles can be fitted with an underbarrel grenade launcher, the FN 40GL-H and FN 40GL-L, designed specifically for the SCAR rifles. The FN EGLM can also be attached to the SCAR.
The SCAR features a foldable stock that is fully adjustable for length of pull (6 positions), and an adjustable 2-position cheek piece.
The weapon is completely ambidextrous; the charging handle, though integral to the bolt carrier, can be on either side of the weapon, the selector switch can be engaged from both sides, and the magazine release can be used from either side. Magazines drop free from the rifle, like the AR-15 and AR-10. The 5.56 NATO SCAR uses STANAG magazines.
The SCAR utilizes the short-stroke gas piston mode of operation; the bolt locks into the barrel extension by rotation when the bolt carrier group closes on the chamber. When the weapon is fired, the gas from the fired round enters a gas port drilled in the barrel and travels through a gas tube, impinging upon the actuator rod, which pushes on the bolt carrier. This unlocks the bolt, allowing the BCG to cycle rearward, extracting and ejecting the spent case from the fired cartridge. Of note is that the unlocking process is not abrupt; the fired case, which expands upon firing and obturates, molding itself to the chamber, has time to shrink again. This reduces the incidence of stuck cases and aids greatly in extraction, which reduces the chance of an extraction-related malfunction.
Civilian variants lack the full auto function.