LSAT Light Machine Gun The LSAT light machine gun , of the LSAT ( Lightweight Small Arms Technologies ) program , is a developmental light machine gun . The program started in 2004 with the Joint Service Small Arms Program ( JSSAP ) and will replace the light machineguns already in operation like the M - 249 SAW and the M - 240 Description . The LSAT Lightweight Small Arms Technology program was initiated by US Army early in 2000s , as an attempt to significantly reduce combat load of the infantrymen , especially those carrying the Squad Automatic Weapons / light machine guns , such as M249 SAW . In around 2004 the ATK corporation was selected as a prime contractor to develop appropriate small arms system , which would necessarily include new , lighter ammunition and a gun ( guns ) to fire it . Initial intent was to develop a caseless ammunition ( which provides maximum savings in the weight and size ) , with a fall - back option for polymer cased ammunition with telescoped design ( in this design bullet is fully ' buried ' inside the powder charge within the simple cylindrical case ) . By the 2010 , ATK successfully developed both caseless ( CL ) and cased telescoped ( CT ) ammo , and several prototype weapons to fire it . The CT ammunition and guns currently are most developed , and show average 41 % weight and 13 % volume reduction when compared to the standard 5 . 56x45 NATO ammunition . The caseless ammo shows somewhat better numbers , but it is also more expensive and , as of now , remains on earlier stages of development . Current plans are to deliver 8 LSAT machine guns and 100 000 rounds of CT ammunition to US Army by May 2011 , for initial assessment . Additionally , ATK recently displayed the LSAT carbine , which fires same CT ammo from 4 - row detachable box magazine , holding 42 rounds . The carbine is still in early development stage . According to the ATK presentations at NDIA 2010 symposium , the manufacturer is ready to scale the LSAT system up for more potent and promising calibers in 6 . 5 - 6 . 8mm range , but not until specifically asked to do so by the US Army . Current ( mid - 2010 ) documents suggest that it is possible to see first units equipped with LSAT small arms system by 2016 . The ammunition for LSAT weapons is made in the form of simple cylinder . Caseless ( CL ) ammunition is made from formed propellant , with bullet located inside and primer glued to the rear . Case telescoped ( CT ) ammunition uses cylindrical cases , made from plastic . Ammunition weights now 8 . 3 gram ( CT ) and 6 . 3 gram ( CL ) compared with 12 . 2 gram for 5 . 56mm M855 . Plastic machine gun links weigh 0 . 5 gram instead of 2 . 0 gram for steel . This results in combat load of 600 linked rounds weighting 9 . 4 kg with standard M855 ammo , and just 5 . 8 kg with CT and 4 . 6 kg with CL ammo . Ballistics of both CL and CT ammunition is similar to the 5 . 56mm M855 , and similar bullets are used . The LSAT machine gun uses gas operated action with gas piston , located below the barrel . It operates oscillating chamber , which swings sideways to eject spent case and load a fresh one , and then swings back in line with the barrel to fire the round . Feed is from specially designed disintegrating belts with plastic links . It has a quick - change barrel and fires from open bolt , in full automatic and semi - automatic modes . Basic design of the weapon remains the same for CT and CL versions , although special measures are taken to provide gas seal between barrel and chamber in caseless version of the gun . The LSAT carbine uses same ammo , but the feed and moving chamber design are different . LSAT carbine is fed from high - capacity , 4 - row box magazines , which are inserted from below the gun . Upon loading , the moving chamber is dropped down below the barrel , so the fresh case can be forced rearwards from magazine and into the chamber . This also forces the spent or misfired case to be pushed out of the chamber and then fall out of the gun . Once the round is fully chambered , action forces the vertically sliding chamber up and in line with the barrel , and the gun is fired .