Hi there - here are going to be a collection of analysis and viewpoints on various fluff points within the 41st millennium. You might have seen me around the forums, and would probably gather that I have some pretty vivid ideas on the setting. I thought it would be good to get my ideas and vision of 40k written down and recorded.
Here is the first of what I've got - let's start at square one, the weapon which I love most about the 41st millennium, which encapsulates so much about this setting's methods, reality of warfare and development of technology - massive scale, absolute overkill, no compromise.
Weapon of saints and angels, traitors and tyrants, the fate of the Imperium has always been linked to those who wield this roaring weapon of human supremacy.
Firing high explosive rocket-propelled cannon shells (‘bolts’), a boltgun is capable of threatening most targets on a battlefield. The Adeptus Astartes are most efficient with the weapon, for its major drawbacks (weight and recoil, maintenance intensity and ammunition availability) are all mitigated by their physical size, strength and the chapter’s superior artifice capabilities. The superhuman marksmanship and advanced optics every Space Marine possess also enables them to use the weapon to its full anti-material capability, and at ranges exceeding what normal combatants would be expected to be efficient.
Boltguns are characterised by their two-stage propellant system, using a mid-power initial charge to conventionally launch the bolt from the chamber, after which a solid-fuel rocket in the projectile ignites and burns for most of its flight. This accelerates the round to supersonic speed as it leaves the barrel, and ensures a flatter trajectory and sustained velocity without the encumbrance of a longer barrel or greater initial recoil. To prevent ignition thrust disrupting spin-stabilisation or setting the projectile off course, the second-stage rocket ignites while the bolt is still moving down the barrel. The exhaust of the rocket firing within the weapon is usually vented directly through the ejection port as the weapon cycles, as well as gas ports drilled down the length of the thick barrel to the end of the muzzle (ref. rocket-propelled shells, ext‘gen1baneblade’, ‘demolisher’).
Unless utilising specialist ammunition and attachments, the visual and acoustic signature of a boltgun is very distinctive and noticeable. The percussive thunderclap of the initial propellant is staggered with the roar of rocketry and sonic crack of the round accelerating a split second later, producing a deafening report of rapid, rolling thunder. Each shot flings a spent casing and produces a characteristic blast of venting exhaust from the ejection port. A mushroom of fumes erupts from the muzzle ring and a noticeable smoke trail is left as the round streaks into the distance.
Given the two-stage propulsion system, performance of a bolt over its flight is more consistent than similar conventional munitions – marginally slower at close range but preserving kinetic energy and penetrative power over distance. On weapons for lesser combatants (e.g. Imperial Stormtroopers), the two-stage system is largely used to lessen the recoil impulse to a practical degree. By significantly reducing initial propellant charge for greater warhead or second-stage rocketry, recoil of even large projectiles is manageable – at the cost of range and/or close-in penetrative power.
For the Adeptus Astartes, such measures are unnecessary, significant recoil mitigated by their superhuman biological strength, artificial muscle bundles and gyroscopic stabilisation of their power armour, as well as the sheer mass of both the boltgun itself (often heavily armoured and stressed for melee use) and the Marine holding it. These last two factors are also central as to how Astartes are even able to use the weapon in void warfare. In frictionless vacuum and zero-g, lighter combatants would be propelled uncontrollably in the opposite direction with each shot. Astartes, simply by dint of their considerable mass require much more force to shift as noticeably and their boltguns, uncomfortably heavy for any mortal to carry, further dampen impulse. The delayed two-stage nature of the propellant also reduces severity compared to a conventional shell, and all power armour gives further consideration to the issue with auto-corrective venting thrusters and mag boots.
In the 41st millennium, most boltguns use a mechanical action to eject spent cartridges and chamber a new round. Methods vary, but usually involve channelling the force of the gasses produced during firing (Godwyn pattern long-stroke piston, Hesh pattern short-stroke, etc.), or a heavy recoil blowback operation (open-bolt blowback Angelus-pattern sub-bolter). It is well-understood on how to placate the simple machine-spirits in these designs, and such procedures can easily be performed in the field. More ancient or advanced models may instead rely on an electrically fed and operated system, a miniaturisation of principles still common in many marks of Heavy Bolter. In such cases, servos controlled by electronics provide the motive force to actively pull rounds into the chamber and cycle the action, allowing a variable rate of fire on a continuous scale. However, when miniaturised into a personal weapon to be used roughly in close combat (as the Adeptus Astartes are wont to do), the electrics are temperamental, more prone to being damaged and offended to a degree that will require specialist ministrations to their outrage.
Bolt shells may be either spin or fin-stabilised, cased or caseless, each feature with its own advantages and drawbacks. The majority created today are metallically-cased and spin-stabilised via a rifled barrel – making each round simpler in temperament and easier to machine and consecrate en-masse. However, the high-powered ignition of each bolt’s rocket within the barrel quickly degrades rifling; regular maintenance rites at the machine shop level are required to prevent decay in accuracy and power.
Caseless ammunition in comparison is smaller and lighter (allowing carriage of more rounds), and is most conducive with self-stabilised bolts, fired from a smoothbore barrel with either rigid fins which flip out or unfurl as the round leaves the muzzle, or angled exhaust ports on each bolt which impart spin. Dispensing with the need to maintain rifling allows a barrel to last much longer, but such ammunition can also be expected to be more intricate, require more care when handled and demand higher tolerances in their artifice. In the modern age caseless ammunition is relatively uncommon - though there is archaeological evidence to suggest such designs were the majority used in ages past.
On contact with the target, the damage potential of a common bolt is produced from its armour-piercing mass-reactive high-explosive payload. The relative complexity of this personal munition is an effort to maximise stopping power regardless of enemy protection level or bodily fortitude.
Mass-reactive fusing is a catch-all term for a variety of solutions which ensure that the bolt pierces and detonates within a target, while avoiding over-penetration (aided at close range by the slower first-stage velocity compared to conventional ammunition). Common fusing methods include timed-delay on impact, upon crush deformation of the projectile body, or even sophisticated machine-sensing (electromagnetic, thermal, etc.) to detect surrounding mass. As with most such things in the modern age, the simplicity and loyalty of the residing machine-spirit is preferred when meditating on the mechanism to birth.
Regardless of fusing, a hit anywhere on a human combatant wearing Munitorum-standard M.40 flak armour with carbifibre plate inserts has been empirically shown to result in a casualty rate of 98.7%, with the wound inflicted being classed as fatal 97.52% of the time (see ref. Rho-Alpha BL564, for Adeptus Mechanicus statistical sample dated 222.M.39-222.M.40). The kinetic energy of the large-calibre round is significant, able to punch the adamantium tip through flak armour with ease to detonate within the vitals. A hit anywhere in centre mass results in explosive coring of the subject, guaranteeing a fatality through spectacular destruction of the chest/torso. Even ‘glancing’ shots that hit extremities have a similar fatality rate (94.23%) – kinetic force and/or explosive detonation destroy the limb, causing massive attendant hydrostatic shock effects to the rest of the body along with the blast wave and fragmentation cone. Against completely unarmoured targets, over-penetration is still an occurrence at close range, even with proper fusing. However, the violent impact and passage of the large bolt alone is usually enough to incapacitate most organisms so fragile.
Even if the round fails to directly connect or penetrate, the close detonation of deflected and partially-penetrating bolts can stun or stagger armoured infantry not prepared for the impact. Against light infantry, a single round's fragmentation and blast effects can incapacitate multiple closely-packed enemies. Many civilian and most natural structures are also not proof against the boltgun – such cover is easily penetrated and rapidly degraded by the explosive power of multiple shells.
This damage potential carries over when encountering heavily mechanised foes. Astartes demi-squads armed with nothing but boltguns have been observed single-handedly blunting and even stopping multi-platoon armoured assaults, in defiance of all mortal military convention. While not able to outright destroy main-line armoured vehicle, boltguns are still potent anti-material weapons in the hands of the Adeptus Astartes. Whether close-in or from a distance, the Marines as infantry are able to use battlefield terrain and superior sensory awareness to avoid the restricted and predictable sight-lines, weapon orientations and movement of buttoned-up vehicles. Their infantry silhouette and sheer speed makes them difficult to sight and track with heavy weapons capable of incapacitating them, as they rapidly reposition between bursts of pinpoint fire. Aiming for tracks, vision ports, sensory clusters, exposed crew and delicate weapons, they leave armoured columns immobile, insensate and uncoordinated. In such a state vehicles are effectively out of the battle, forced to disengage if able, or allow the Astartes to close in to slaughter the crew and ensure their destruction with grenades and melee weapons.
In short, the power afforded to a Space Marine by a full-size Godwyn pattern boltgun (there are numerous sub-calibres taming the weapon for mortals) can be approximated to rapid-fire light vehicle cannon – but with the handiness of a compact auto weapon and the accuracy of a designated marksman’s anti-material rifle. Given the firepower and flexibility a mere squad is afforded with these weapons, one can only imagine the thunderous power once unleashed by the fury of the Legions.
You might have noticed I have failed to mention the exact calibre of the holy boltgun. While official figures sit at 0.75cal (~20mm) I believe this is a too small size if we wish to maintain their iconic proportions as depicted in all 40k artwork to date. 20mm is far too small in proportion to the barrel or the Marine holding it. This is illustrated well in an article done a while ago by one of our Frater.
The above article posits an upscale to .998cal (~25mm) to partially solve this size disparity, based in part on a misinterpretation of a 3rd ed. schematic (it labels the gun as belonging to the year .998, not its calibre). I however believe this is the correct sentiment if we wish to retain the visual heft of the boltgun as envisioned by GW over 30 years. In addition, I believe the ‘official’ 20mm is at the barely-acceptable level in power for Space Marines to be effective, given their relative rarity and when compared to their opponents in both 30k and 40k.
Obviously, this requires Heavy Bolters (officially sitting at a flat 1.00cal/25mm) to also be enlarged. I say 40mm, based on the sheer heft they have in iconic art. And going further up the line, many say that ‘autocannons’ are equivalent to a modern 40mm Bofors autocannon. But look at the size difference in barrel between a pred/hydra with an actual 40mm. (the Ajax AFV, UK's new armoured cav scout, 40mm cannon main gun).
They look like sticks in comparison to an Imperial armoured vehicle scale - they're too small. I always thought the ‘autocannons’ of the 41st millennium are more like clip/autoloader-fed rapid-fire HE 76mm Sherman guns. That’s more like it. I play a homebrew ‘truescale’ 40k ruleset, and have autocannons pegged as Blast weapons.
Edited by SpecialIssueAmmo, 30 November 2017 - 10:12 AM.