M4
Your absoluely correct anything can be abused.
One poster mentioned the heavy 30 cal machine gun.
The water cooled browning heavy.
Run out of water or mess up the tube and you can overheat that too.
so far it's one of the few .
If you really need lots of rounds then use the gatteling gun
The BAR was shot in 6 round or 3 round bursts.
The 30 air cooled 1919 A4 and A 6 was shot maximum 30 seconds .
That's about one belt of 250 before a new box of ammo.
That got hot really quickly also. That's why the asbestos glove and the new barrel
Headspacing was easy and quick.
The new Saw {squad automatic weapon] is for sustained auto shooting.
You can overheat that too.
The 16 is fine it just needs a face lift
I need the surplus ammo too.