The Ultimax 2000 is a Singapore-made 5.56mm light machine gun prototype, developed by the Chartered Industries of Singapore (ST Kinetics), and is extremely accurate due to its constant-recoil operating system. The Ultimax 2000 is a gas-operated fully automatic weapon with a short-stroke gas piston operating system and uses a locked breech design with a rotating bolt. It fires from an open bolt position and has a non-reciprocating cocking handle located on the left side of the receiver that stays in the forward position during firing. 

This unit has two barrels with one with a matching serial number and the other marked "TW7 SPARE BARREL."  This prototype was modified to use standard AR-15 magazines.

Click Here for a video from TFB TV about the Ultimax 2000.