The FN FNAR is a gas-operated semi-automatic rifle, with the short-stroke gas piston located below the barrel, within the stock. It features an internally chromed barrel, an aluminum receiver, and a polymer stock with a pistol grip. It is chambered for a 7.62x51 NATO cartridge and uses a detachable box magazine with a capacity of 5, 10, or 20 rounds. There are no preinstalled sights. Instead, the FN FNAR has a Picatinny rail for mounting sights. There are three variants, the FN FNAR Standard, FN FNAR Heavy, and FN FNAR Competition. All of them have a 20-inch barrel and a two-stage trigger. The FN FNAR is compatible with the standard 10-round SX-AR magazine.