The Roles and Weapons with the Squad

[120mm]

There's more to a weapon than the cyclic rate, muzzle velocity and carried weight. Before the M249, there was an attempt to use an M16A1 with a bipod as the squad automatic rifle.

Machine guns take more of a beating because sustained automatic fire is hard on a gun. The M249 is heavier because it's built to handle that work. The belt feed also means a lot less time spent reloading vs a twenty or thirty round magazine.

Not that I necessarily have an informed opinion on which is the better choice, but I do believe the M249 is not completely irrational. It's simply a different set of tradeoffs.

Exactly. Any machinegun that requires a sustained rate of fire needs to be heavier than a rifle.

But I'm liking what Wilf says about that theoretical "sustained" rate of fire at the fire team level. I think a "real" machinegun is a better choice, with a "real" machinegun round and rate of fire. And your automatic rifle can be a piston gun with a drum.