Sticking together is important.

However The Guide frowns upon the use of Heavy Machine guns dude to inaccuracy during long periods of automatic firing. They're also a big ammo eater. More accurate kills can be accomplished with half the ammunition and even less noise and more accuracy. You cannot silence an M249, You can however, silence an M4A1

Keep it on Semi-auto rather than Fully automatic, only click that bitch to "Rock n' Roll" if you absolutely need to output high amounts of fire. I suppose you could just burst fire methods with Machine Guns to maximize accuracy and cut down on ammunition consumption. They're heavy fuckers too... wouldn't wanna lug that thing around PLUS the ammo box.

I'm cool with a Thompson, however they do make a rattling sound when you shake them, could be a problem for Night operations and stealth maneuvers.
The rattling has something to do with the action of the gun, not sure what.
You would also be carrying ammo for a separate weapon, say a Colt M1911 ?