(note: not mine, but i needed a quick picture to get the idea across).
the heavy MG is a weapon designed specifically for the purpose of mowing down several units at once, or providing suppresive fire. a heavy MG does both.
to use, it is quite simple. the heavy MG has a 12" range, and attacks all targets within a cone of fire (hooray fingercones!). to determine damage, it is as follows. first, make a successful skill roll (over 4) against targets in the cone. then, do 1d10 - (fingercone) points damage. EXAMPLE: a two finger cone is 1d10-2 damage, 3 fingers is 1d10-3, etc. if a target is taking the entire blunt of the attack (this means that at both cone ends, the target overlaps), then you do double damage. the downside of this weapon is that it requires a turn to set it up (open up the tripods, etc), but the payout is worth it.
HMGs also provide suppresive fire. any unit caught within the cone for longer than one(1) turn is suppressed. this means they can't take any action other than movement, and even that is reduced by 1d4 inches.
in a similar vein, miniguns follow the same rules, but with 1d12-(fingercone) damage instead. they also take a full turn to warm up, but minifigs can walk while firing them (at 1" per turn).
any of these weapons can be made bigger and put on vehicles by using standard "multiply by weapon size" rules, except range is only increased by 6" for each size up.
In any case, the rules are nice as I've stated in the topics actually made for them. I mainly came here to pick on your choice of gun. Their actually the rules I used to mulch bunches of Dan's guys during Armageddon. See the front page for the battle.
