The FN Minimi, as stated before, uses a 5.56x45mm NATO round fed by a 30 round STANAG magazine, 100 round drum, or a 200 round belt. It can share ammunition with any 5.56×45mm NATO firearm and is lighter than previous light machine guns, which fired the heavier 7.62×51mm NATO round. The barrels have a quick-change capability; a lever is provided on the left side of the weapon that unlocks the barrel allowing the shooter to push it forward removing it from its trunnion. A carrying handle is also fixed to the barrel and assists in the barrel change process. The pawl-type feeding mechanism is modeled on the system used in the FN MAG. The belt is moved in two stages during both the forward and rearward movement of the reciprocating bolt carrier, which provides for a smooth and continuous feeding cycle. The feeding mechanism top cover features a device that indicates the presence of a cartridge in the feed path. Magazine feeding is used only as an auxiliary measure, when belted ammunition has been exhausted. The ammunition belt is introduced into the feed tray, magazines are seated inside the magazine port at a 45° angle, located beneath the feed tray port. When a belt is placed in the feed tray it covers the magazine port. Likewise, a magazine inserted into the magazine well will prevent the simultaneous insertion of a belt. The magazine port, when not in use, is closed with an L-shaped hinged flap equipped with a tooth, which engages a corresponding opening in the magazine and serves as a magazine release.
Variants of the FN Minimi are used by the U.S. (FN M249 SAW) and the U.K. (L110A1). A 7.62×51mm NATO variant exists as the Maximi.