bound by teir tactical-esque ammo: Each uses it's own ammo type.
M-100 Grenade launcher
It's more of a dumbfire rocket launcher(It is, actually). Does have a slight homing trait. One shot, one ammo used. Max is 10.

ML-77 missle launcher
Homing missles. Uses one ammo per shot, max ammo is 16.

M-622 Avalanche
Shoots a projectile that creates a freezing feild. Think winter's howl from call of duty, but much, MUCH bigger. Max ammo is 20, one used per shot.

M-920 Cain
It's a nanonuke. It starts out at 10% charge. Picking up a heavy weapon charge(Can't get HW ammo from weapon piles) Boosts the charge by 16. Can be fired when it hits 100% or above. Max is 200%.
If you need a better explanation:
http://www.youtube.com/watch?v=p4b-8glzVAgWARNING:THIS WEAPON MAY CAUSE MASS DEATH. DO NOT USE IN TIGHT SPACES.
Collector particle beam
It shoots a beam. Full auto, uses 5 ammo per second. Max ammo is 549. you get 190 ammo per charge.

M-490 Blackstorm
Shoots a gravity well. Rips up bricks and opponents (Provided if their sheilds, barriers or armour is do- Wait. Okay, only picks them up if they have 25% health or less.)
Max ammo is 5.

M-451 Firestorm
It's a flamethrower. Exact same ammunition consumption and max capacity as the particle beam. Stuns enemies if you burn them.

Arc projector
Little induvidual damage compared to the other HW weapons that don't have an AOE(Except the cain). It has a slight charge up, but when it's charged, it shoots a bolt to the target, and this bolt jumps to nearby enemies after that. Max ammo is 10. Uses 1 per shot

Side notes:
-The cain and it's ammo, if put into a weapon shop, would be pretty expensive. It's like this in the actual game: You are only usually able to fire it once every other mission... Unless you get to 200% charge.
-In mass effect, they all use power cells, But that may be hard to implement in BL, so they may have their own unique ammo types.
-If possible, when put away, they should be put on the players back and folded up (Like, appears on back in full but starts collapsing into a folded up version)
-The cain is not as destructive as the mini-nuke (And the cain's explosion is twice or 3 times the size of the default RL)
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Wiki article if you need it: http://masseffect.wikia.com/wiki/Heavy_Weapons