The secret lives of Bolters.

Bolters – a study into the internal, external and terminal ballistics of the most iconic weapon of the 41st millennium.

1) Classification.
The ‘Bolter’ family is wide and diverse, ranging from the Bolt Pistol, the standard side arm of the Adeptus Astartes to the Vulcan Mega Bolter, a Titan mounted anti infantry weapon. What can be said to link all of these different weapon system? The key component in any Bolter class weapon is its ammunition. Bolt shells, regardless of their calibre, contain a micro rocket motor and a warhead (of many designs), making them more akin to a rocket propelled micro-grenade than a conventional bullet or artillery shell. Calibres of Bolt shells vary according to the weapon systems using them. The smallest shell of note was then 12.5mm micro deluxe round used in custom Bolt Pistols for high ranking Imperial Guard officers, the largest was 125mm ‘Vulcan Delta IV’ as used in the Mars D4 pattern Mega Bolter.

We shall be focussing on the classic bolter in this article, yet even this weapon is often misclassified by scholars, being called everything from a rifle to a sub machine gun and everything else.

Firstly a rifle is such named due to its ‘rifled’ barrel, the adding of spiral grooves to the barrel to impart spin on the round, stabilising it in flight. Many Bolters are smooth bore, so calling it a rifle would be incorrect.

A sub-machinegun is generally defined as an automatic weapon firing a pistol cartridge. As the Bolter fires its own, unique rounds, this can not also be correct.

The most commonly accepted definition is that of a ‘Heavy Assault Carbine’. Carbines, generally, have been shorter and lighter than rifles, firing a lighter cartridge to reduce felt recoil. The Bolter fits into this category with its shorter barrel and lighter recoil (for its calibre). Bolter rounds are certainly not less powerful than regular autogun rounds but due to the method of propulsion a classic bolter would produce less recoil as there is no charge to propel it out of the barrel, only its own rocket. The ‘Heavy Assault’ prefix to the carbine is in reference to the Bolters heavy rounds and sustained fire capability.

If you look at the normal usage of a Bolter by the Adeptus Astartes you will find that is generally used in the same situations the would call for Carbines for the Imperial Guard: shorter range engagements where the rapid deployment of sustained fire is more important than long ranged, accurately placed single shots.


2: Ammunition.
It is a common error to think that Bolters only come in a single calibre, or even a small range of calibres. A logistics survey of the 7th Darius crusade in M38 was fortunate enough to be given permission to inspect the weapons of an Imperial Fists Demi-Company (half of the esteemed 1st company, no less!) This survey revealed that most of the Marines carried their own, personal, weapon that had been in their use for an average of 35 years and had been in use by the chapter for an average of 120 years. The oldest weapon was forged in M34 (though had been modified many times) and the newest weapon was less than 3 years old (Terran Standard) having only just completed its ritual blessings and firing ceremonies and being used for the first time in battle. Between this range of weapons over two dozen different cartridges were present varying in calibre, length, weight and other characteristics. Many Marines carried Bolt Pistols that used the same calibre Bolt Shell as their Bolters (with both weapons accepting the long standard magazines and the shorted ‘pistol’ magazines) though one individual was found to be carrying 3 different shells with him, one for his rifle and one each for a pair of Bolt Pistols given to him by his Captain 50 years ago in recognition for an undisclosed act of valour. It would appear that the inconvenience of supplying units with no standard ammunition is not an issue of the Adeptus Astartes, instead they rely of the bond between each warrior and his own weapons.

It has been found that for each calibre of infantry weight Bolt Shell manufactured there will generally be the full spread of Bolt Weapons able to fire it, from the Bolt Pistol through the Bolter and Storm Bolter all the way to the Heavy Bolters. The calibres found varied from the (previously mentioned) 12.5mm micro deluxe (generally only found in Bolt Pistols and gatling format Heavy Bolters) through to the 30mm Obliterator class shell (found in the relic weapon from M34). The 3 most common calibres were the 19mm Mars pattern (also called the .75), the 17.5mm Wolf (both long and short) and the 20mm Armageddon cased round.

As mentioned there were often more than 1 Bolt Shell in a given category, most commonly a longer and shorter version (equivalent to regular and ‘Magnum’ shells for hand guns) and in some instances there were cased and caseless ammunition.

This brings in another common misconception about Bolter ammunition, that is always caseless. This will be explained in the next section.


3: Internal and external ballistics.
As has already been mentioned the defining characteristics of a Bolt Shell is the rocket base and a warhead capability. This rocket base is the defining characteristic of the flight of the Bolt Shell (its external ballistics).

The advantage of a gyro jet round is that it allows the weapon to fire a relatively heavy round with little or no recoil, allowing a soldier to carry a weapon for more powerful than normally possible. It is because of this that some Imperial Guard officers are able to carry the weapon,s all be it in much lighter calibres than the soldiers of the Adeptus Astartes.

The firing cycle of a classic Bolter is fairly simple, the mini rocket in the shell is electronically activated by the pulling of the weapons trigger. The rocket ignites providing thrust which accelerates the round out of the weapons barrel and towards the enemy. The 19mm Wolf round has a rocket rated at 15Kj meaning it increases the kinetic energy of the round by around 30000 Joules per second. The rocket burns for 1 seconds meaning at the end of the burn cycle the round has 30 KJ of energy, meaning the 125 gram shell is travelling at almost 700 meters per second.

The round will be stabilised in one of 3 ways, either by rifling on the barrel (which is rare), by retractable fins that spring from the round when it has left the barrel or, most commonly, by the angle of the jets which propel it.

One issue with gyrojets is that at vary short ranges there is not enough time to allow the round to accelerate to a useful velocity. It takes over 450 meters for the round mentioned above to reach its maximum velocity. At ranges of 100m (quite common for the close range fighting Marines often have to undertake) the round has only accelerated to around 415 meters per second and thus will have only a third of its final kinetic energy. At ranges of 10m, for room to room fighting, the shell is travelling at under 200 meters per second with less than a twelfth of its maximum energy.

As a result many Bolter weapons systems use a hybrid cartridges which contain both a gyrojet and a normal powder charge. These weapons often use cased ammunition to contain the charge though some weapons use solid blocks of propellant and remain uncased. Due to the charge in the case the Bolt Shell will carry less propellant, typically burning for half the time of a classic Bolt Shell (around half a second).

To get any noticeable muzzle velocity for such a heavy round a considerable charge is needed and as a result only the enhances strength of a Space Marine is enough to use these weapons, but as very short range fighting is their speciality it is very common to see them use cased bolter ammunition.

A typical cased Bolt Shell might have a muzzle velocity of around 500 meters per second, giving the weapon formidable punch and point blank range (thought the recoil this produces is around 8 times that of an autogun, completely unmanageable for an infantry weapon if it were not for the Space Marines’ enhanced strength and Power Armour). With this initial boost the round will have achieved its maximum velocity (700 meters per second, slightly less than the classic Bolter Round) in only 300 and at 10m will have over 6.5 times the energy of a classic bolter round.

The use of the cased bolter rounds sacrifices maximum velocity/energy and low recoil against effectiveness at short ranges. Pressing the barrel of a bolter armed with classic gyrojet only Bolt Shells to the head of an enemy will result in only mild bruising (or catastrophic barrel damage if the round detonated upon impact). With a cased round there is enough velocity to cause horrific injuries even at point blank range but the massively increased recoil makes the weapon harder to use at anything over a hundred meters range. By balancing the amount of propellant in the case and the amount of fuel in the Bolt Shell it is possible to custom build a set of ammunition with ideal ballistic characteristics for a specific mission.

It is for the above reasons that many members of the Imperial Guard consider Bolters to be caseless weapons yet almost every example seen of Marines firing their weapons shows spent cases being ejected from their Bolters.


4: Ammunition.
It is true that a warrior must always select the correct weapon for a task. With a weapon platform as versatile as the Bolter a warrior must also select the correct ammunition. In this section we shall look at some of the more common ammunition types in the Bolt Shell family.

Most of the rounds described below are available across the full spectrum of calibers, in both long and short as well as cased and uncased rounds.

The Kraken Penetrator class of rounds is used mainly against heavily armoured targets or very large targets where extreme depth penetration is required.

The Kraken round contains a micro RPD (radio proximity detector) which emits a tiny radio signal from the tip. When the round gets to within a critical distance of the target the reflected signal is strong enough to activate the detonator. This premature warning of detonation allows the warhead to activate with a ten thousandth of a second of impact. A substantial shaped charge detonates behind a copper penetrator tip which both propels the copper forward at supersonic velocities and turns it into a jet of plasma. This then burns a hole through whatever it comes in contact with, recording significant damage to even adamantium and ceramite plates (traditionally the best defense against plasma attacks). Against plasteel and armourplas plates the plasma jet is hot enough to burn through even the thickest infantry armour and damage the target underneath.

Against organic matter the Kraken Penetrator has limited affect. Moisture in body tissue rapidly absorbs the heat of the plasma causing horrific burns to surrounding tissue but significantly reducing the penetration potential. Against human targets these wounds often prove incapacitating but not fatal (unless a shot affects a vital organ near the bodies surface). Against more robust targets, such as Orks, the Kraken Penetrator has proved to be disproportionately ineffective.

The Metal Storm round is the chosen ammunition for ‘soft’ targets, those not wearing or possessing thick armour. The round is encased in a thin ceramite sleeve which is marked into hexagonal sections. An inertial sensor in the round detects the impact of the round and then after a fraction of a second detonates the warhead. This delay is adjustable allowing the user to compensate for larger and smaller targets as well as the targets armour. When the warhead detonates the pre-scored ceramite case shatters and turns into dozens of pieces of ultra-hard, ultra-sharp fragments which tear through the targets soft tissue and can even snap bones. It has been noted on several occasions that secondary casualties can occur from fragments flying out of the primary targets corpse.

The Metal Storm round has a second innovative firing mode. Like the Kraken round it contains a RPD. The user can activate the RPD allowing the round to detonate in the proximity of targets (normally 1 or 2 meters). This creates a cloud of supersonic fragments that can affect multiple targets in a similar way to a well places scatter shot from a shotgun round. The Metal Storm round has the advantage of deploying the fragments at a significant distance from the firer allowing the engagement of targets far outside of shotgun range,

The Metal Storm round, ideal against light targets, lacks penetration capability against heavy armour. This has led to the development of a multi-purpose round.

The Dominion APAP round (armour piercing anti personnel) is a hybrid between the Kraken and the Metal Storm round. The RPD is removed and the copper penetrator is replaced by a pointed adamantium core. The round maintains the ceramite shell but both the forward facing shaped charge and the fragmentation warhead are reduced in size.

The round must be set into one of two modes before firing, either armour penetrating or anti personnel. In the armour penetration mode the shaped charge is detonated upon impact propelling the adamantium core forward. This super hard core has sufficient energy to penetrate a significant amount of armour but its low cross section means it causes limited damage to flesh, it is most likely to pass through the target cleanly. Against soft targets the round is set to detonate its primary charge shortly after impact having passed into the targets body cavity. In anti personnel mode the weapon is very effective against body tissue but has limited armour penetration capabilities.

Against armoured targets a 2-1 burst is favoured. The first two APAP rounds are set to armour piercing, hopefully seriously damaging the target’s armour, the third anti personnel round should then be able to pass through the armour and into body tissue to cause fatal damage. If the 3rd round does not pass fully through the armour the detonation of the frag warhead should be enough to open a larger hole in the armour allowing the next burst to finish the round.

There are many specialist rounds and wareheads available, from silent rounds for stealth missions, incendiary rounds, radio tagging rounds and so on but the Kraken, Metal Storm and Dominion represent almost 90% of rounds fired by a typical Bolter in a military campaign.


5: Specialist and rare shells.
A number of less orthodox ammunition types are available across the Bolt Weapon platform, a number of which I shall describe below. The Bolt Shell is an incredibly versatile munition for infantry, its large volume allows a heavy warhead to be delivered accurately over long ranges with a good rate of fire. A well trained artificer may be able to make any number of custom shells for specific purposes.

Hellfire shells.
This is one of the more horrific rounds available to the forces of the Imperium and its use is strictly controlled, primarily due to the psychological affects upon the user. Hellfire shells utilize a biochemical acid to dissolve organic matter creating catastrophic tissue damage that is almost always lethal. These shells saw their first significant action when it was found that certain Tyranid splinter fleets had evolved resistance to viral weapons. A previously unused bio weapon was released for testing by the Ordo Xenos and found to be remarkably efficient against Tyranids (and all other species for that matter).

The warhead is replaced by a glass shell containing the hellfire serum. When the round impacts the glass shatters and slivers coated in the serum are driven into the targets body. The mutagenic acid is exceptionally fast acting, attacking the DNA in the target causing rapid cell breakdown, reducing the victim to a bubbling pool of decaying organic matter in a matter of seconds. This is harrowing even for battle hardened soldiers so the issuing of Hellfire shells is limited almost exclusively to Ordo Xenos kill teams, though some Astartes chapters have their own, limited, supplies.

Psyk Out (Psycannon) Shells.
These shells are incredibly rare, possibly the least common ‘standard’ shell in the Imperium. They are used exclusively by members of the Inquisition and their attached forces when dealing with Daemonic entities and psykers. Psyk Out shells can be fired from any Bolt class weapon though the Psycannon has been designed especially for the purpose. It should be noted that most of the time Psycannon fire regular Bolt Shells, the Psyk Out shell is reserved for times of absolute need due to its rarity.

The manufacturing process for these rounds is a closely guarded secret of the Adeptus Custodes who make them and supply them to the various orders of the Inquisition. It is widely rumoured that the key component of the shell is a by product of the operation of the Golden Throne. This has not been confirmed but the reverence shown to these rounds by the Inquisitors who use them would be an indication that the rumour may not be far from the truth. The warhead of a Psyk Out shell consists of a small chamber of Fenthyionic crystal (the material used in the construction of Psyhic Hoods) to contain the powers of the weapon. This chamber is further encased in a micro Geller Field to totally isolate it from the Warp. When the round impacts the target the crystal chamber shatters and the geller field loses its integrity, unleashing the mysterious core component.

The effects of Psyk Out shells depend on the target. If it is fired at a non psychic or non-Daemonic entity the round has little or no effect other than the kinetic energy it carries. Targets have been observed to be disorientated after being hit and suffering some hallucinations and paranoia, but nothing that would warrant the extreme cost of the shell. Against psychic or Daemonic targets the round has a much more pronounced affect. The active component in the shell contains a vast amount of psychic energy which overloads and warp sensitive beings. This will overload and shut out any psychic abilities a user may have and can sever the link to the warp needed for Daemonic entities to survive in real space.

Inferno Bolts.
These rounds are used exclusively by the Sorcerers of the Thousand Sons traitor legion. None have ever been recovered so their construction can only be estimated. When the round strikes its target there is an observable temporary real space/Warp space overlap, releasing the malignant energies of the Warp into the area around the target. Some scholars have speculated on an inversed Geller Field creating this weakness but others, including myself, believe that some foul sorcery is in play.

Vortex Bolts.
Only one example of a Vortex Bolt has ever been observed in the Imperium, in M38 in the hands of a Rogue Trader by the name of Davith Pentacall. He claimed to have had the rounds, of which he had only one left, custom manufactured by a Xenos race of unknown identity. He was unable to give out any more information even after questioning from the Ordo Xenos who took a dim view on his consorting with aliens. He was duly executed with the same round that condemned him, demonstrating its power. When the round struck a micro vortex opened creating a 1m sphere of Warp Space that persisted for nearly 0.3 seconds the collapsed with a significant shock wave. This killed him, his executor, and the judge and jury from his trial.

Melta Bolts.
I was privileged enough to spend time with Tech Priest Aharmen of Mars who was very keen to show me the area of research he had dedicated his last 300 years to. Using newly recovered STC data he was making a design of Bolt Shell with a micro melta charge in the warhead. Using a RPD to time detonation on impact the small warhead was capable of penetrating even the heaviest armour if it struck square on. Magos Aharmen claimed to have a 40% detonation success rate, which he was very proud of, and showed one the test firings he had completed and recorded. The video showed a combat servitor with a modified Heavy Bolter engaging a Land Raider from one of the Traitor Legions (presumed Iron Warriors but not confirmed). The servitor waited until the tank had driven parallel to his position, at a range of around 100 meters, then unleashed a sustained burst of fire. The rounds stitched a line from just in front of the left Lascannon weapon mount and up, through the weapon until it hit the upper track guard. Detailed analysis shows that out of the 40 shots that hit the tank only 7 resulted in detonation of the melta charge, though this was enough to disable the tanks left track unit and destroy the Lascannons on that side of the vehicle. Using the right side tracks, which were still operational, the tank then turned to face the servitor, who began another heavy volley of fire across the face of the tank. This has a better success rate with 20 of the 50 shells detonating, destroying the front mounted Heavy Bolters, the assault ramp opening mechanism and the right hand side track unit. Unable to turn and without a firing angle from its remaining Lascannons the enemy tank was effectively neutralized. The test can not be considered a full success though as the tank was not destroyed and its cargo, a unit of Traitor Terminators, disembarked from the starboard access hatch and vaporized the servitor with their Reaper Autocannons.


6: Ammo Feed and Supply.
Bolt weapons face a significant difficulty over the more primitive stub weapons when it comes to ammo feeding. Bolt Shells are disproportionately heavy for the calibre of the weapon firing them, making them awkward and difficult to feed into the breech, especially during higher rates of fire. In addition to this, with classic bolters the gyrojet provides virtually no recoil and very little exhaust gasses with which to power the loading cycle. As a result all Bolt weapons have motorizes power feeds. The same technology that made Power Armour possible and drives the ferociously powerful Chain weapons allows artificers to manufacture very small yet powerful motors that have found applications in almost every area of warfare in the 41st millennium. The ability to have motorised ammunition systems in infantry weapons allows an unheard of rate of fire, even for high calibre weapons, with excellent reliability.

Bolt Weapons, despite the large size of their rounds, utilise high capacity magazines for most of the available models. This is due to their primary users, the Adeptus Astartes, being able to handle such heavy clips without difficulty. Imperial Guard and Inquisitorial officers often use lighter rounds and lower capacity magazines but still the magazines are heavy and cumbserone.

Most weapons accept a variety of ammo feed systems from drums to box magazines. A typical Bolter magazine may be straight (normally for un-cased rounds) or slightly curved (for cased rounds) and holds around 30 rounds. Longer and shorter magazines are common but it is rare to see a magazines of more than 45 rounds due to the additional strain placed on the feed motor. High capacity drums are available, holding between 80 and 120 rounds. These drums contain additional feed motors that have the force push the rounds through the mechanism.

Some older weapons have the capacity to accept belts of ammunition. A string of Bolt rounds is fed into the weapon, normally from a box clipped to the base of the weapon though sometimes from a back pack. These weapons require a special add-on to ‘de-link’ the rounds as they are fed into the weapon. Belt fed weapons have the advantage of much higher ammo supply (up to 500 rounds in a belt) but are more prone to jamming, especially if the belted rounds get dirty.

The favoured weapon of the terminators of the Adpetus Astartes, the Storm Bolter, has a unique ammunition feed problem. As Terminators are unable to reload their weapons in combat they have to carry a high capacity magazine with the weapon. As a result they normally use a box of linked ammunition or a double capacity drum. Loads of over 200 rounds are not unusual



7: Bolt Weapon Format.
This article has mainly focussed on the standard Bolt Gun. This weapon is fairly compact for its calibre but still is very large for a regular Guardsman. The weapon is perfect for the Adeptus Astartes, is good rate of fire and the lethality and versatility of its ammunition make it perfect for their main role as a shock troop. The weapon usually has a removable or collapsible stock to aid in medium and short range engagements making it comfortable to shoulder fire (the size of a Marine combined with the benefits of power armour allow this with the large recoil from the cased shells).

Aiming a Bolter is done either visually (using the simple flip up sights or an attached scope) or through an optical feed linking the weapon to a display in any tactical helmet. Many weapons carry a triple configuration laser dot sight to help with aiming, especially when hip-shooting. The first two lasers emit an invisible beam that converges at a range of 2km. A sensor then monitors where the dots are on a target, allowing a small logic engine to accurately calculate the range. The third laser, projecting a visible beam, is then angled to compensate for drop at the given range.

Firing mode can be selected manually or via a datalink connected to the users tactical suite in their armour. As Bolter utilise electronic ammunition activation there is no need for a mechanical safety, just an ‘off’ setting and a variable fire rates. Controls are normally included for adjusting the fusing/settings of some ammunition types, these two can be set via the user’s tactical suite. If no settings are specified then the ammunition will automatically set itself to the manufacturers default settings. Rate of fire and length of burst size are also variable with most Bolters capable of firing around 420 rounds per minute as a maximum. Most users tend to settle for 3 or 4 rounds per second as a manageable rate of fire.

Bolters are designed to be fired using both hands but some Chapters of Marines have taken to using special pistol grips than let the fire the weapon single handed. This obviously reduces the accuracy of the weapon and is not recommended but the strength of a Marine in his Power Armour seems to be enough to use even these most massive weapons with ease.

Bolt Pistols are the next most common weapon in the Bolt group, commonly used by many areas of the Imperium. Some weapons are fitted with a mini stock, making them more like micro-carbines than pistols. Bolt Pistols are capable of automatic fire, and are frequently used in such a way by Marines though Imperial Guard issue Bolt Pistols are generally semi automatic only.

Bolt Pistols are surprisingly popular with Imperial Guard officers and Commisars. Due to the short range use of pistols Bolt Pistols only ever use cased rounds. Even with lower calibres and reduced powder charges (sometimes giving a sub-sonic muzzle velocity) the recoil these weapons produce can be overwhelming, I have interviewed many officers hospitalised by their own weapons. For un-enhanced or non power armoured soldiers the Bolt Pistol seems to be a very poor choice, it is very heavy and difficult to fire. The popularity they have is not based on their power but their image. Commissars have long used Bolt Pistols to execute unworthy Imperial Guard officers and as such the weapon has a mystique and respect attached to it that marks the wielder as an officer of both valour and ability.

Heavy Bolters are one of the most common Heavy Machine Guns in service in the forces of the Imperium. There are two classes of Heavy Bolter although one is less favoured and becoming more rare. In most cases a Heavy Bolter fires substantially larger Bolts, at least 25mm and sometimes as large as 60mm. These rounds can be cased or uncased but in the cased variety use a smaller propellant charge to keep the recoil manageable, even for Power Armoured users. This size of Bolt carries a large warhead and makes the Heavy Bolter one of the most versatile weapons available.

The other class of Heavy Bolter is much older and is was created as a spin off from the same program that developed the Combi Bolters and Storm Bolters. It was found that by using a very powerful feed system cased Bolter rounds could be fired with an alarmingly high cyclic rate if adequate recoil compensation was built into the weapon. The resultant weapons were the first Heavy Bolters and were capable of firing standard calibre bolts at a rate of almost 1200 rounds per minute. Several models have been manufactured, some experimenting with twin or even Gatling configuration. Ultimately is was decided that the increased rate of fire was not adding much value over the standard Bolter and so the pattern of Heavy Bolter with a heavier Bolt became more common.

Bolt Weapons and Suspensors.
Adeptus Asartes and Bolters seem to have been designed to be used together but Bolt Weapons are still popular amongst regular Humans. To compensate for their weight and recoil some users have fitted suspensors to their weapons. These micro antigrav units can reduce the felt weight and, if correctly fitted, can provide forward thrust to the weapon to compensate for its recoil. This is a complicated fitting as if the timings are wrong the user will still feel the full force of the recoil and then have the weapon pulled out of their hands. Suspensors, although fairly common on larger equipment, are very rare and costly to manufacture in the size where they can be fitted to infantry weapons. As a result of this many suspensors are more valuable to the weapons they are fitted to (even in the case of the ever costly Bolt weapons). Although not confirmed, it is believed Commisar Yarrick had his Storm Bolter fitted with a suspensor as he was able to fire a full size, cased round Storm Bolter with his only hand.