Except for the ones that don't. Like those ones firing 40mms. Also, the rounds are individually more effective, due to several explosive charges having been detonated before the front bullet has left the barrel, increasing the muzzle velocity when firing in bursts or at an otherwise high rate.
40mms are not bullets. We do not want an uber-fast grenade launcher in this game. We want an uber-fast machine gun. Thus we are basing it off the Metal Storm gun. However it has a capacity of basically a normal rifle and then you reload it. So it's kind of pointless. Take the 3GL. Ten bullets and then a reload at increased muzzle velocity does not beat 100 bullets a second at constant speed, unless you reload 10 times a second, and unless your bullets are going so ridiculously fast that each individual 5.56 mm round is like a 20mm round, three or four times larger - which seems quite unlikely to me, using such overpowered firepower on mere enemy personnel would be a waste. Wouldn't they advocate using the 3GL on tanks instead, if they were that powerful?
Also, several of the Metal Storm rounds get fired before the gun recoils. Think about that for a minute.
So it's accurate? Well then, we probably shouldn't include it in the MG category at all, neh?
Proposal: Epic Weapons.
Nobody's even gotten a class weapon yet. Epic weapons are epic, but they're flashy and essentially useless. It's fun to think about but I don't see a point to adding even more weapons that will either never be used, be used commonly and make the game essentially as it was (except everyone does 1000 damage with each shot), or be used uncommonly and make the game unplayable unless you have an Epic Weapon.