i'd say it's a 3-sec 6 shot burst for the GL.... and... i'll not even mention that shot...machineguns's rate of fire ^^
i bet ~75 years would make a hand-held version of this quite possible, too: http://www.youtube.com/watch?v=wHf_vMd5MOQ&feature=related
but it's a game about aliens invading earth, so i'm not looking for that much realism anyways
well we've been able to make machine gun that much faster than modern ones do for decades but if the size of the magazine hasn't increased enough to make much increase is weapon rate of fire worthwhile. shifting to caseless ammunition with increase mag size slightly so could support a higher rate of fire. but not likely to change much.
just look at the
HK G11 developed during the 1970s and 1980s.
Cartridge 4.73x33 mm caseless ammunition
bullet mass 3.25 g
Rate of fire 550 rounds/min full auto, 2200 rounds/min 3 round burst
Muzzle velocity Approx. 930 m/s (3,050 ft/s)
Effective range 400 m
Feed system 45 or 50-round detachable box magazine
2200 rounds a minute but with a 50 round mag that means it can discharge it's entire magazine in 1.4 seconds. hence it being limited a quarter of it's maximum rate for full auto.
rate of fire isn't everything