Chaingun/Doom

The chaingun (also known as "gatling gun") is a rapid-firing, multi-barrelled automatic weapon. It uses the same ammunition as the pistol, and is fed from the player's shared stock of bullets.

The chaingun is first found in a secret area of E1M2: Nuclear Plant, and again in a secret area of the following level. It then appears in a non-secret area on E1M4: Command Control. In Doom II, it is first found on MAP03.

The chaingun contains 20 rounds of ammunition when picked up (40 on the "I'm Too Young To Die" and "Nightmare!" skill levels). In Doom II, chainguns taken from fallen heavy weapon dudes contain 10 rounds (20 on the "I'm Too Young To Die" and "Nightmare!" skill levels) and, unlike pre-existing chainguns, disappear when crushed beneath doors or moving ceilings.

Combat characteristics
The chaingun always fires in pairs of hitscan shots, as long as the player has two bullets or more. Each bullet inflicts 5-15 points of damage. The first two shots in a volley will always be exactly on target, but if the trigger is held down, later shots will suffer from the same dispersal as pistol shots (standard deviation around 2°, to a maximum of ±5.5°).

The chaingun's rapid rate of fire means that a single enemy caught in its hail of bullets will have little or no chance to retaliate. This is effective against most monsters, particularly demons and cacodemons (but not boss monsters, whose pain chance tends to be very low). The weapon is also highly effective at mowing down hordes of zombies or imps. Because its recoil does not affect the first two shots, it is an ideal weapon for sniping, as the player can tap the fire button for accurate two-shot bursts. The chaingun is also good for finishing off monsters that have been weakened by attacks from more powerful weapons.

However, under most circumstances, ammo consumption must be carefully monitored, as the chaingun's relatively high rate of fire can deplete one's ammo quickly, especially since many of the more powerful monsters can take literally dozens of bullets to kill. In particular the player's inventory only allows for a limited supply of bullets compared to other types of ammunition, plus bullets are scarce compared to shotgun shells. For general combat, the slower-firing (but more powerful) shotgun is usually preferred, allowing the player to stockpile bullets for situations where the chaingun's high rate-of-fire is useful.

Data

 * 1) This table assumes that all calls to P_Random for damage, pain chance, blood splats, and bullet dispersal are consecutive. In real play, this is never the case: counterattacks and AI pathfinding must be handled, and of course the map may contain additional moving monsters and other randomized phenomena (such as flickering lights). Any resulting errors are probably toward the single-bullet average, as they introduce noise into the correlation between the indices of "consecutive" calls.
 * 2) In the case of continuous fire, the target must be close enough to compensate for the weapon's recoil.
 * 3) Assumes that direct hits are possible, which does not occur in any stock map.

Demo files

 * [[Media:Map07-chaingun-tapping.lmp |Chaingun "tapping"]] technique (file info) being demonstrated on MAP07: Dead Simple.

Appearance statistics
The IWADs contain the following numbers of chainguns (excluding those from fallen heavy weapon dudes) per skill level: