The Tech-priests of the Adeptus Mechanicus and the skilled Artificers of the Adeptus Astartes have developed many types of Bolter Ammunition, simply called "bolts," over the millennia for the different branches of the Imperial military that use Bolt Weapons. The most common variants are described below.
Bolter weapons are relatively common in the Imperium of Man and come in different sizes, from handheld Bolt Pistols to the mighty Vulcan Mega Bolter mounted on super heavy tanks and Titans. The Standard Bolt Round is set to .75 calibre, whereas Heavy Bolter rounds are larger, at 1.00 calibre. An even larger calibre is used in the Mauler Pattern Bolt Cannon of Castellax Battle-Automata. The Vulcan Mega Bolter mounted on the Macharius Vulcan variant of the Macharius Heavy Tank utilises Heavy Bolter shells, whilst the far larger ones mounted on Titans and Stormlord tanks fire projectiles the size of human skulls.
Whereas conventional solid slugs utilise a propellant charge contained in a casing that forces the bullet down the barrel upon ignition, in contrast, a bolt is self-propelled; it features its own integrated solid fuel propellant that propels the bolt at high speeds, essentially acting like a miniature rocket. The propellant itself is shaped to control the bolt's direction and speed; however, this method of rocket propulsion would normally warp the barrel due to gas pressure. The Bolter uses an ingenious two-stage method to prevent this.
As well as the rocket propellant, a small conventional charge is also utilised. This charge is strong enough to force the bolt out of the barrel at a significant muzzle velocity, and simultaneously ignite the bolt's propellant. The rocket-propellant is precisely fused to ignite immediately as the bolt leaves the barrel, alleviating any possibility of pressure build-up. The bolt then accelerates toward the target under its own power.
The .75 calibre is now the standard for bolts in the late 41st Millennium. However, during the early days of the Great Crusade in the late 30th Millennium, there were Bolters that made use of variable calibre ammunition. This included the ancient Tigris Pattern Bolter, which fired .60 calibre bolts, and the Phobos Pattern Bolter, which made use of .70 calibre bolts. The ancient Space Marine Legions' archaic Ikanos Pattern Bolt Pistol made use of a .50 calibre bolt.
Standard Bolter ammunition utilises a mass-reactive fuze, designed to penetrate the target before detonating within, maximizing damage to the target and leaving little chance for survival.
Standard Bolt Rounds
In Bolt Rounds, a tiny amount of conventional explosive charge is utilised alongside rocket propellant. This charge is just strong enough to force the bolt out of the barrel and ignite the bolt's propellant. The rocket-propellant is carefully fused to ignite just after leaving the barrel, alleviating any possibility of pressure build-up. The bolt then accelerates away towards the target under its own power. Standard Bolter ammunition is designed to penetrate the target and then detonate, causing immense damage and leaving little opportunity for survival.
The standard Bolt Round consists of:
- A solid-fuel rocket propellant base
- An outer casing containing conventional charge
- Mass-reactive fuse. Has a split-second timer to delay detonation upon impact until after the shot penetrates the target.
- Hardened diamantine penetrating tip. This allows for the bolt to penetrate most armour before detonation.
- Main Explosive Charge
- Dense metallic core. This is a very dense material, adding weight and thus momentum to the round when in flight. This aids in the bolt's penetration of the target.
Hellfire Rounds have devastating results on organic matter, as the rounds were developed to combat the Tyranids. The core and tip are replaced with a vial of mutagenic acid with thousands of needles that fire into the target upon the shattering of the vial, pumping the acid into the foe. They were originally developed to be fired as single specialised rounds by a Heavy Bolter with an area of effect, but have also been downsized for standard calibre Bolters, where they function as direct-impact penetrators instead.
Stalker Silenced Rounds
Stalker Silenced Shells are Bolter Rounds that possess low sound signatures, intended to be used for covert combat and sniping. These rounds are best used in conjunction with an M40 Targeting System and an extended barrel on a Stalker-pattern Bolter, to produce an effective sniping weapon system. A solidified mercury slug replaces the mass-reactive warhead for lethality at subsonic projectile speeds. A gas cartridge also replaces both the propellant base and main charge for silent firing.
Inferno Bolt Rounds
Inferno Bolts are designed to immolate their targets and destroy them with superheated chemical fire. The dense core of the standard Bolt is replaced with an oxy-phosphorous gel, derived from Promethium. It should be noted that despite having the same name, Imperial Inferno Bolt rounds are unrelated to the Inferno Bolts used by the Chaos Space Marines of the Thousand Sons Traitor Legion, which are actually psychically-bound slugs that release arcane energies upon impact. These energies react explosively with a living target, but not against psychic Blanks or inanimate objects.
Ulysses Bolts are bolts which contain a tracking device. Fired into large objects, this type of bolt will accurately report the target's relative position to a hand-held tracking device.
Metal Storm Frag Rounds
Metal Storm Frag Rounds are best used against multiple lightly-armoured targets. They detonate before impact and spray shrapnel, shredding their victims. A proximity detonator replaces the mass-reactive cap, and the diamantine tip and dense metallic core are replaced with an increased charge and fragmentation casing. They are similar to flak rounds and are used against large clusters of enemies.
Kraken Penetrator Rounds
Kraken Penetrator Rounds are powerful armour-piercing rounds. The dense metallic core is replaced by a solid Adamantium core and uses a heavier main charge. Upon impact, the outer casing peels away and the high velocity Adamantium needle accelerates into the victim, where the larger detonator propels shards of super hardened metal further into the wound. These rounds are effective against heavily-armoured infantry and lightly-armoured vehicles.
- The main charge is increased to enable a larger explosion.
- The standard dense metallic core is replaced by a core of pure adamantium to optimise the penetration of reinforced armour.
Psycannon Bolt Rounds
Psycannon Bolts are used by the Inquisition, primarily the Ordo Malleus and the daemon-hunting Space Marines of the Grey Knights. They are very similar in nature to the rounds fired by their namesake, the Psycannon, and are similarly potent against psychic and daemonic targets.
Banestrike Bolt Rounds
These mysterious variant bolt shells, believed to have been designed in secret within the armouries of the Alpha Legion long before the outbreak of the Horus Heresy, had it seems a sole purpose; to breach the Ceramite Power Armour of Space Marines. Used openly for the first time at the Drop Site Massacre on Istvaan V in 006.M31, their dense explosive cores and firing stresses reduced their range and swiftly degraded the firing weapon, but their effect against the betrayed Loyalist Legions were devastating. Fortunately for the Loyalists, supplies of these difficult to manufacture munitions were limited, and only the Alpha Legion and the Sons of Horus were able to field them in substantial numbers beyond that incident of brutal treachery during the Heresy. These shells were primarily utilised by the Legion Seeker Squads of the Alpha Legion or the Reaver Attack Squads of the Sons of Horus.
Bloodshard Bolt Rounds
Bloodshard Shells are large, bolt-shaped shells intended to be fired only by the Angelus Pattern Bolter used by the Sanguinary Guard of the Blood Angels Chapter and their Successor Chapters. Each Bloodshard contains a payload of razor-filament that can shred most known forms of armour upon impact.
Dragonfire Bolt Rounds
Dragonfire Bolts are hollow-shelled bolts used by Sternguard Veterans that explode with a gout of superheated gas that can eliminate the value of cover for enemy troops as any targets struck receive full damage even when partially protected by cover.
During the Great Crusade and Horus Heresy eras of the late 30th and early 31st Millennia, Scorpius Bolts were individually hand-crafted by the Techmarines of a Space Marine Legion's armoury. These specialised shells utilised a two-stage warhead which contained a micro-guidance system and a needle-like sabot dart which vaporised when striking an armoured target, providing enhanced armour penetration effects. Scorpius Bolts were rare and temperamental munitions which were hand loaded into a Bolter for firing.
Seeker Bolts are unique, hand-crafted rounds created by Chaplain Boreas of the Dark Angels Chapter. Each bolt contains a miniaturised Cogitator that detects the infrared heat signature of a target and then steers the bolt unerringly towards it.
Shrapnel Bolts were modified Heavy Bolter rounds utilised exclusively by the Iron Warriors Legion during the Great Crusade and Horus Heresy eras. This speciality ammunition was utilised as a potent anti-personnel weapon and is believed to be the precursor to the Metal Storm Frag Rounds (see above) developed in later millennia. The mass-reactive cap and diamantine tip of Shrapnel Bolts are replaced with a blunt percussive trigger plate, and the dense metallic core is substituted with an additional explosive flechette cluster. The trigger plate in the tip caused the bolt to explode on impact, spraying the target and nearby area with a directed blast of shrapnel from the flechette cluster. This ammunition was available as an option for all units in the Iron Warriors Legion equipped with Heavy Bolters, twin-linked Heavy Bolters or Quad Heavy Bolters.
Tempest Bolts replace the standard mass-reactive core and armour-piercing tip of a bolt round with a fragmentation shell encasing a powerful micro-explosive proximity charge. This has the effect of showering a target with a murderous storm of shrapnel. These heavier rounds, however, lack range compared to standard bolt shells. Produced only on Mars, Tempest Bolts were designed to be particularly effective at incapacitating machines and other electronic devices. Such bolts are highly effective against targets like combat robots and cyborgs whose bodies are now more machine than organic tissue.
Vengeance Round bolts were created using unstable flux core technology that makes them hazardous to use but extremely potent at penetrating through heavily armoured targets. As their name implies, these bolts were developed by the Imperium specifically to target the Chaos Space Marines of the Traitor Legions. They are equivalent to the ancient Banestrike rounds developed and utilised by the Alpha Legion Traitor Legion against the Loyalist Legions during the Drop Site Massacre on Istvaan V.
Utilised by Deathwatch Kill-teams, these precious rounds were developed using an unknown technology to help prevent Necrons from "phasing out" and returning to their Tomb complexes. In this way Imperial forces can ensure that even their undying foes stay dead.
Stable Flux-Core Bolts
In 992.M41, an ancient datacache was unearthed upon the jungle planet of Johan's Eden. The Adeptus Mechanicus descended upon the world, only to find the planet's modest populace slain by Necron Canoptek constructs. Several Mechanicus war congregations launch a simultaneous attack. Eight standard years of war follow before the Cult Mechanicus recovers the datacache. Three intact STC designs are recovered as a result -- one for self-heating cookpots, one for parchment autoquills, and one for stable flux-core bolt rounds that can melt ceramite as if it were wax just like Vengeance Rounds, but without the danger implicit in their use.
As well as the different types of ammunition available for the weapon, there have also been several different types of magazines. The standard magazine for the Bolter is the Sickle Magazine.
- Sickle Magazine: The standard-issue magazine, seen on most Bolter patterns. The magazine's shape is slightly curved to allow rounds to stack more neatly, thus taking up less space for a higher capacity magazine. Carries 20 to 30 bolts.
- Straight Magazine: A straight version of the sickle magazine. Holds less ammunition (only 10 to 20 bolts), but is easier to load in more intense situations.
- Drum Magazine: Drum magazines are a relatively rare sight in the 41st Millennium. This is due to their unreliability; drum magazines have an unfortunate tendency to jam. However, drums can carry 40, 60 or even 100 bolts, negating the need to reload as often. Despite the frequent jamming, they still brook some favour with local Hive Gangs or planetary defence militia. They are also frequently seen on Storm Bolters or in brutal assaults, where running empty in a firefight can mean certain death.
- Belt Feed: Some troops forgo using magazines at all, preferring to feed the bolts directly into the firing chamber using a linked belt. Because the belt is exposed to the elements, it is frequently clogged with dirt or dust. This can, like the Drum Mag, lead to jamming, and is rarely used within the Imperium, although it is very commonly used by the Chaos Space Marines. Note that Space Marine Heavy Bolters have the ammunition belt protected by a tough, flexible feed chute; while the servants of the Ruinous Powers sometimes use a box magazine to house their ammunition belts.
- Duplus X: This type of magazine is quite popular amongst local planetary law enforcement or Hive Gangs. It involves two standard Sickle Magazines which are attached together by some means, usually a band of cloth or tape (similar to the "ready-mags" of ancient Terra). This means when the weapon has to be reloaded, the user can simply flip the magazines around and insert the loaded magazine. This type is rarely produced.
- Codex: Adeptus Mechanicus - Cult Mechanicus (7th Edition) (Digital Edition), "The Quest for Knowledge - The Scouring of Johan's Eden"
- Codex: Blood Angels (5th Edition), pp. 50, 59
- Codex: Dark Angels (4th Edition)
- Codex: Daemonhunters (3rd Edition), pg. 18
- Codex: Grey Knights (5th Edition), pg. 55
- Codex: Imperial Guard (5th Edition), pg. 88
- Codex: Space Marines (7th Edition) (Digital Edition), "Armoury of the Space Marines - Special Issue Wargear - Special Issue Ammunition", pp. 447-448
- Codex: Space Marines (5th Edition), pp. 63, 88, 100, 118
- Codex: Space Marines (4th Edition), pp. 1, 11
- Codex: Witch Hunters (3rd Edition), pp. 19, 22
- Dark Heresy: Blood of Martyrs (RPG), pg. 114
- Dark Heresy Core Rulebook (RPG), pg. 133
- Dark Heresy: The Inquisitor's Handbook (RPG), pp. 109, 148, 171, 173
- Deathwatch: First Founding (RPG), pp. 97-98
- Deathwatch: Rites of Battle (RPG), pp. 134, 140
- Imperial Armour Volume Two - Space Marines and Forces of the Inquisition, pg. 101
- Imperial Armour Volume Three - The Taros Campaign, pp. 49-50
- Imperial Armour Volume Four - The Anphelion Project, pp. 126-128
- Imperial Armour Volume Nine - The Badab War - Part One, pp. 60, 86, 91, 94, 102, 120, 128
- Imperial Armour Volume Ten - The Badab War - Part Two, pp. 65, 71, 76, 86, 115, 128, 133
- Index Astartes III, pg. 58
- Rogue Trader Rulebook (RPG), pg. 122
- Rogue Trader: Into the Storm (RPG), pg. 112
- The Horus Heresy - Book One: Betrayal (Imperial Armour), pp. 19, 230, 232
- The Horus Heresy - Book Two: Massacre (Imperial Armour), pg. 209
- The Horus Heresy - Book Three: Extermination (Imperial Armour), pp. 251, 259
- Warhammer 40,000 - Apocalypse War Zone: Damnos, pg. 18
- Warhammer 40,000: Wargear (4th Edition), pg. 8
- Warhammer 40,000: Wargear (2nd Edition), pp. 21, 35
- Warhammer 40,000 Rulebook (6th Edition), pp. 54, 56
- Warhammer 40,000 Rulebook (3rd Edition), pg. 60