Chaingun

The chaingun occupies weapon slot 4 in the classic Doom arsenal, slotting between the shotgun and the rocket launcher as the player’s primary sustained-fire option. Where the shotgun delivers concentrated burst damage and the rocket launcher handles crowd control with splash, the chaingun bridges both roles through sheer volume of fire — spraying hitscan bullets at a rate that can stagger or outright kill many mid-tier demons before they mount a counterattack.

The chaingun’s early history

The chaingun was already present in Wolfenstein 3D, the game id Software released immediately before Doom, and Doom likewise included the weapon alongside the pistol. An early version of the Doom chaingun appeared in the press release beta, where its graphic differed from the final version. In particular, the barrel tips stopped short of the barrel band rather than extending past it as they do in the released game. Despite its name and appearance, the Doom chaingun is not a true chain gun. The chaingun’s in-game images draw its look from the “Ol’ Painless” Tootsie Toy Gatling Gun, a motorized, electronic toy Gatling cap gun, while a real chain gun uses a single barrel and an electrically driven chain mechanism to cycle its action.

Combat mechanics

Every trigger pull from the chaingun produces two hitscan shots in pairs, so long as the player has at least two bullets available. Each individual bullet deals between 5 and 15 points of damage. A notable property of the weapon’s accuracy model is that the first two shots in any volley are perfectly on target — no dispersal is applied. If the trigger is held continuously, subsequent shots suffer the same spread as pistol fire: a standard deviation of approximately 2° with a ceiling of ±5.5°. This behavior makes the chaingun surprisingly viable for long-range sniping when the player taps the fire button rhythmically rather than holding it down, producing accurate two-shot bursts each time.

The reason exactly two shots remain accurate is tied directly to the classic Doom source code. A_FireCGun calls P_GunShot with accuracy determined by the refire counter; that counter is still 0 for the first two chaingun firing states and is only incremented by A_ReFire, so a fresh tap resets the accuracy. The inaccuracy itself comes from two random values being subtracted and shifted in P_GunShot.

The rapid rate of fire — 525.0 shots per minute in the original game — means that a single enemy caught in sustained chaingun fire will frequently be interrupted mid-animation, cycling through its sprite frames so rapidly that it appears to shuffle and spin. The Doom instruction manual named this effect “the chaingun cha-cha.” Beyond the cosmetic curiosity, the practical implication is meaningful: enemies with a meaningful pain chance, such as imps, cacodemons, and demons, will spend most of their time in pain states rather than attacking, effectively neutralizing their threat so long as bullets hold out.

Ammunition economy

The chaingun draws from the same shared bullet stock as the pistol, meaning every bullet picked up anywhere — including clips, bulk ammo boxes, and those recovered from fallen zombiemen and shotgun guys — feeds the chaingun. A chaingun picked up directly as a floor item provides 20 rounds, or 40 on the “I’m Too Young To Die” and Nightmare! skill levels. Chainguns dropped by fallen heavy weapon dudes yield only 10 rounds (20 on ITYTD/NM) and, unlike placed weapons, vanish if crushed beneath a door or moving ceiling rather than persisting as pickups. The maximum bullet capacity is 200 rounds, expandable to 400 when the player carries a backpack.

First appearances across IWADs

Aside from the locations listed above, chaingun also appeared in Doom 64, with its first encounter in MAP02: The Terraformer. In deathmatch, it appears as early as E1M1: Hangar and MAP01: Entryway respectively.

Doom 64 variant

The Doom 64 iteration of the chaingun carries several distinguishing characteristics. Visually, it features longer perforated barrels and a worn blue finish rather than the polished steel of the PC version; its pickup sprite has a somewhat rusted appearance. In terms of performance, the Doom 64 chaingun fires at 600.0 shots per minute — faster than the original — and deals 4–16 points of damage per bullet rather than the 5–15 of the classic version. When fired, the screen jerks up and down rapidly, adding a kinetic feedback absent from the PC release. The muzzle flash also differs: Doom 64 uses a smaller blue flash compared to the continuous bright flash of the PC version.

In the modern games

Doom 3 reimagines the weapon as the “UAC Weapons Division Mach 2 Chain Gun.” It has a roughly half-second wind-up before firing and uses dedicated .30-calibre belt ammunition rather than the classic Doom bullet pool. Its belts hold 60 rounds, while a chaingun dropped by an enemy provides 30 rounds.

In Doom (2016), the chaingun is the Delta-12, a high-velocity heavy weapon that fires 15 mm tungsten slugs. Unlike Doom 3’s version, it begins firing as it spins up rather than waiting for the barrels to reach full speed.

Doom Eternal removes the spin-up delay altogether, allowing the chaingun to fire at full speed immediately. It shares its ammunition pool with the Heavy Cannon and adds the Energy Shield and Mobile Turret weapon mods.

Port variations and a known bug

The chaingun behaves somewhat differently across ports. In the Sega Saturn version, it fires significantly faster than in other releases. In PSX Doom, the firing animation changes so that the muzzle flash blinks rather than remaining continuous as in the PC original.

The chaingun is associated with one well-documented engine bug: when exactly one bullet remains, the chaingun fires that bullet normally, but the engine plays the firing sound (DSPISTOL) twice instead of once. The root cause lies in the A_FireCGun function, where S_StartSound is called before the ammunition check, causing the extra sound even though only one bullet is consumed. Some source ports have fixed this bug, although some deathmatch players have noted a minor gameplay implication of doing so.

Tactical role

Against the full roster of Doom’s enemies, the chaingun performs reliably across a wide threat range. Zombiemen and barrels fall in roughly two shots on average. Imps and cacodemons require more sustained fire but remain pinned by pain states throughout. Demons and spectres demand a longer burst. Boss-tier enemies — the cyberdemon and spider mastermind — have very low pain chances and thus are not effectively stunlocked; against them the chaingun serves better as a damage-dealer of last resort than as a crowd-control tool.

The weapon also appears prominently in tapping techniques where the player fires brief two-shot bursts to maintain perfect accuracy while conserving ammunition. This approach is especially documented on MAP07: Dead Simple.