gas adjustment valve) that allows the rate of fire to be controlled and enables reliable operation in various environmental conditions. The gas regulator is usually pre-adjusted prior to operations. Where there is sluggish operation due to fouling, the gas setting may be increased by two clicks using the provided C-tool. The weapon features a standard pistol grip, a vertical forward grip integrated into the forend and a detachable buttstock. The mild felt recoil allows the weapon to be used effectively without the buttstock, using only the pistol and forward grips to support and aim the firearm. The adjustable bipod has a height adjustment mechanism and is secured to the weapon's forend, providing stability in a sustained-fire role. The bipod is quick-detachable and can be mounted or removed without the use of tools. The Ultimax 100 features an aperture type rear sight (with range settings for distances up to 1,200 m, graduated every 100 m) placed on a sliding scale and a forward vertical post housed in the front sight base and protected by two metal tabs. The weapon incorporates sheet metal stamping and the use of synthetic components in its design. The drum magazine, buttstock, pistol grip and forend with vertical grip are all made of an impact-resistant polymer. The Mark 3/3A can fire both the American 5.56×45mm M193 cartridge (with 1:12 (305 mm) twist barrel fitted) or the heavier SS109/M855 cartridge (178 mm (1:7 in) twist rate barrel). Mark 4: Developed for the United States Marine Corps Infantry Automatic Rifle program, with the addition of a new fire selector module. The Marine Corps did not select the Ultimax and chose an automatic rifle based on the HK416. Mark 5: Updated variant of the Mark 4 with a folding stock, Picatinny rails and M16 STANAG 4179 magazine well that will accept 30-round box magazines and the 100-round Beta C-Mag drum. STK also developed a vehicle-mounted variant of the weapon for use on the Bronco All Terrain Tracked Carrier and on the Spider Light Strike Vehicle. Mark 8: New variant unveiled at the 2012 Singapore Airshow. Users : Adopted to replace Colt M16 HBAR LMGs. : Chilean Marine Corps, replaced in 2014 by the Heckler & Koch MG4. : Komando Pasukan Katak (Kopaska) tactical diver group and Komando Pasukan Khusus (Kopassus) special forces group. : Used by the SAJ. : Commissioned by the Singapore Army in 1982. : Used by the