Heavy Machine Gun

The Heavy Machine Gun is a mounted weapon featured in Left 4 Dead 2. It is new in the sense that it replaces the Minigun from Left 4 Dead. It fires extremely powerful bullets accurately and operates with a slower rate of fire relative to the Minigun. Ammunition is unlimited. Unlike the Minigun, there is no wind-up time and it fires the instant the trigger is operated.

The HMG can fire continuously for 15 seconds and takes one minute to cool down if it overheats.

The only sign of overheating is the barrel glowing from orange to yellow hot, indicating that it's about to overheat and any further usage will render it useless for a full minute.

Locations

 * "The Plantation"―Located at the center of the top floor overlooking the garden at the rear of the plantation house. (Mostly useless, since enemies and even tanks usually come from where it is unable to cover)
 * "The Bridge"―Just before the drop-off to the helipad, the Heavy Machine Gun is located on a truck directly opposite the drop down. (Useless, since nobody would need it at that point, aside from survival levels)
 * "The Port"―Used by Louis on the bridge during the finale. It can only be used by players if Louis is kicked via console commands (the command is under sv_cheats: kick Louis).
 * "Port Finale"―Located on the bridge during the finale. It is usable in both Left 4 Dead and Left 4 Dead 2.

Tactics

 * Firing short bursts (rather than holding the trigger down) gives a steady rate of fire and will delay, if not prevent, overheating. Short bursts on demand are possible because there is no wind-up time like the Minigun found in Left 4 Dead.
 * The Heavy Machine Gun, like the Minigun, uses the crosshair of whatever weapon (melee, guns or items) the operator is currently holding. In gameplay, this seamless transition makes aiming the Heavy Machine Gun easy and instinctive, but has no effect on the weapon's accuracy. The weapon's crosshair expands and contracts infinitely and automatically thus coping perfectly with targets at all ranges. This effect can be used to change the crosshair of the Heavy Machine Gun to best suit the player's preference or play style, helping players fire more accurately without improving the accuracy of the gun itself.
 * AI Tanks are programmed to attack the player operating the Heavy Machine Gun. This feature can be used to the Survivors' advantage in two ways: Firstly, AI Tanks can be drawn into a "killing zone" whereby they are overwhelmed by concentrated interlocking fire from the gun and other teammates. Secondly, AI Tanks can be drawn away from threatened teammates by mounting the Heavy Machine Gun.
 * The Heavy Machine Gun is in a favorable position in the finale of "The Sacrifice". It is placed on the bridge, allowing the gunner to cover the entire intersection plus the generator area, possibly allowing the sacrificing Survivor to live long enough to restart the generator. The gun's location is also out of reach for most Infected. Furthermore, AI Tanks will also attempt to target the HMG, not the sacrificing player.
 * However, to make it happen at least 2 human players are required, as bots will not do the sacrifice.
 * In "The Port", the Heavy Machine Gun manned by Louis is very helpful when trying to achieve "Kite Like a Man".
 * In The Plantation, the gun is on a balcony overlooking a hedged garden. However, very few (if any) Common Infected attack from that direction and from angles covered by the gun. Players choosing to defend from this position can try to improve their chances by throwing bile bombs down into the area covered by the gun and hope that the Tanks will spawn in the same area.
 * Though, in the Survival Guide trailer, Rochelle fires it from the bottom floor, this is impossible in-game unless the HMG is spawned via concole commands there. It's likely an early-development video.
 * In "The Bridge", the gun appears once the Survivors have accessed the bridge and the end-of-finale phase has begun. It's useful when playing on survival mode.