CIS Ultimax 100 The CIS Ultimax 100 is a Singaporean light machine gun created by the CIS ( Now ST Kinetics ) in 1982 to equip the Singapore Army , the Ultimax 100 is also used in Croatian , Philipines and other armies . Description . In 1978 , an American small arms designer James Sullivan , a man who previously worked for Armalite and participated in design of the AR - 18 assault rifle , traveled to Singapore . There he joined the small arms design team at Chartered Industries of Singapore ( CIS ; now Singapore Technologies Kinetics ) Inc , with task to design a squad automat weapon / light machine gun that could serve as a companion to the assault rifle then in development at the same company . After about four years of development and trials , Singaporean army adopted the new squad automatic weapon , known as Ultimax 100 , in 1982 . Ultimax light machine gun was produced in three subsequent versions ( Marks ) , with fourth being evaluated in USA at the time of this writing ( autumn 2007 ) . The current production version is Ultimax 100 Mark 3 , which is described below . Other versions are as follows : " Ultimax 100 Mk . 1 " was a pre - production variant . " Ultimax 100 Mk . 2 " was the first production gun , with fixed ( non - detachable ) barrel and a folding carrying handle located above the center of the mass of the gun . Production ceased by late eighties , with introduction of the Ultimax 100 Mk . 3 . " Ultimax 100 Mk . 4 " is an updated version of Mk . 3 , developed for U . S . Marine Corps “ Infantry Automatic Rifle ” competition . It features an updated barrel with M16A2 - style flash hider , Picatinny rails on top of receiver , optional for end with additional Picatinny rails on 3 - , 6 - and 9 - o ’ clock positions , and a quick - detachable magazine adaptor for unmodified M16 ( STANAG ) magazines . The new buttstock is of skeletonized design and folds to the side . The trigger / fire control / pistol group is a modular unit , which can produce a variety of firing modes including single shots , three - round bursts and full - automatic fire . Ultimax 100 Mk . 3 is gas operated , air cooled , magazine fed weapon . Ultimax 100 Mk . 3 has quick detachable barrels , equipped with carrying handle to assist hot barrel removal . Each gun is supplied with two barrels , and additional barrels of standard ( 508 mm ) or short ( 330 mm ) length can be obtained from manufacturer ( latest versions also available with optional 267 mm “ VIP Protection ” barrel ) . Gun is gas operated , utilizing short - stroke piston gas system , located above the barrel and fitted with manual gas regulator that has five settings . Barrel is locked using rotary bolt with multiple radial lugs . The patented “ constant recoil ” action is in fact a simple effort to avoid the heavy bolt group slamming against the backstop in receiver . This is done by elongating the stamped - steel receiver ( and available bolt travel path ) and by carefully calculating the strength of return spring . Feed is from detachable magazines only , using either proprietary 100 - round drum magazines or slightly modified 30 - round M16 - type box magazines ( modification involves an additional lock holes for Ultimax magazine catch ) . Drum magazines are made mostly from plastic , with translucent rear wall which permits easy check of available ammunition . Original intent was to make these drums disposable but currently these are reusable . Ejection of spent cartridges is to the right side , and ejection port is covered by spring - loaded dust cover . Firing controls include a pistol grip and a conventional rifle - type trigger ; ambidextrous safety / fire selector levers are located at either side of receiver , above the pistol grip . Gun fires from open bolt only , in semi - automatic or full automatic modes . Standard furniture includes a lightweight folding bipod , attached to the gas block , short polymer forend with forward pistol grip , and a removable plastic butt ( gun can be safely fired with butt removed ) . One somewhat unusual accessory for Ultimax 100 is a bayonet lug on the barrel , which permits attachment of a standard M16 - compatible bayonet . Operators Variants Specifications