The Ultimax 100 is a Singaporean 5.56mm light machine gun, developed by the Chartered Industries of Singapore—CIS by a team of engineers under the guidance of American firearms designer L. James Sullivan.
Work on a new light support weapon for the Singapore Army began in 1978. The weapon is produced by CIS, initially in the Mark 1 version, later—the Mark 2, and currently, only the Mark 3. The Ultimax 100 is used in significant numbers by the armed forces of Singapore, Croatia and the Philippines.
The Ultimax 100, also known as the “Section Machine Gun” is a gas-operated automatic weapon with a short-stroke gas piston operating system powered by ignited powder gases diverted from the barrel through a port in the gas block. The Ultimax 100 is a locked breech weapon with a rotating bolt that contains 7 locking lugs. It fires from an open bolt position.
The bolt contains both a spring extractor and a casing ejector. The weapon’s non-reciprocating cocking handle is located on the left side of the receiver and occupies the forward position during firing. The Ultimax 100 is striker-fired. The feature that grants the weapon its low recoil is the “constant recoil” principle. The overall design allows the bolt carrier group to travel all the way back without ever impacting the rear, instead stopping gradually along the axis of movement against the resistance of the return springs.
The magazine catch consists of two tapered pins on a bar, controlled by the magazine release button. The machine gun feeds from a proprietary 100-round synthetic drum magazine, or from a modified 20 or 30-round STANAG 4179 magazine.
The Ultimax 100 uses a manual safety mechanism that consists of a lever installed on the left side of the receiver with two possible settings: “S” – indicating the weapon is safe and “F” – continuous fire. An internal safety achieved through the proper arrangement of parts and mechanisms secures against premature detonation. The light machine gun was also designed to mount an M16-type bayonet and either day or night-time optics. Ergonomics of the Ultimax 100 are somewhat close to the Thompson submachine gun.