Bulk of ground units have 3 round burst but there are lots of full auto M4's and M16's out there also. I could not fathom burst, kinda pointless.
But then again, full auto is pointless with a few exceptions; breaking contact or conducting an ambush. Otherwise, it's semi auto 99.9% of the time, something the general populace can't seem to grasp; semi is so much more effective than auto, I could care less about auto. I've never used auto on a rifle except in training, it's just not necessary.
full auto (or burst for that matter to a lesser extent) wastes ammo, overheats the gun, more likely to jam (maybe) and is relatively innacurate. You will spend most of your time reloading mags, not shooting. When you have to take a quick shot, I don't want to be reloading!
it's the A1, A2, A3 designation, I don't remember which is what but those will tell whether it is burst or standard full auto. I wanna say A2 is full auto, burst is A3 ??