Bolter firepower analysis thread

[Cykeisme]

Ah, okay.

However, do boltguns eject spent casings?

If they don't, the propellant charge that ignites in the chamber is internal to the shell itself, as the shell travels down the barrel.
Even if it is only lit for a fraction of a second during the shell's travel down the barrel, it's a rocket, ain't it?

[weemadando]

Yes, artwork, schematics and fluff all say that they do eject casings.

As I mentioned previously, Watson's description states that it gives the bolter shell a split second after it leaves the barrel to ignite the rocket-assist. So the bolter isn't truly a rocket-launcer. More like a hand-held Mk-19 firing rocket-assisted rounds.

[Sea Skimmer]

So some thoughts even though I’m not familiar with the bolter descriptions myself. Genade launchers like the Mk19 use a high pressure-low pressure system which is rarely used on other types of weapons. I don’t think they’d use it because it would give the shell less space for HE/rocket fuel for its bulk, and unless part of it discard it would also give inferior aerodynamics. Still, it would be possible to use a high pressure-low pressure system in combination with rocket assist if you really wanted.

Giving the advanced technology available it would also be possible to have the projectile have two separate rocket motors separated by a time delay, one launches it out the barrel with a low velocity push, the second one has much higher thrust and gives it long range and hitting power. The most straightforward way to do things though; would simply be to have a small propellant charge launch the projectile and directly ignite rocket motor. Potentially you could also have a duel thrust rocket motor, which it’s basically the same advantage as two separate rocket stages by varying the fuel mixture in a single solid rocket motor casing.

All of these methods would produce low recoil, but not no recoil. The low recoil might be to the point that the shear mass of the weapon and its user make it almost irrelevant.

[weemadando]

No, all descriptions indicate that it's definitely conventionally fired and then uses RAP to sustain velocity/accelerate to target.

And all bolters have a fairly notable recoil.

[Cykeisme]

Potentially you could also have a duel thrust rocket motor, which it’s basically the same advantage as two separate rocket stages by varying the fuel mixture in a single solid rocket motor casing.

This is what I was thinking, myself.

If first stage of fuel has a fairly steep expansion curve, considering it's firing inside a completely enclosed chamber/barrel, this isn't much differen't from "conventionally firing" the shell.

[Shadowtraveler]

Not sure if this helps, but it's from the Dark Heresy suppliment Inquisitor's Handbook explaining the difference between Astartes and "regular" bolters.

The mighty Adeptus Astartes are superhuman in every way, and so too are their weapons. Each is oversized, specially designed for their great strength and large physiques. This is especially true of bolter weapons such as boltguns and bolt pistols. Massive and reinforced like their users, even the ammunition clips are sheathed in protective wards and armour, with hand-grips larger than any human hand can manage and a weight that would require most humans to use a support bracing. Indeed a human trying to fire such a weapon would likely suffer recoil of such strength that it would rip their arm from its socket. Space Marine boltguns are simply not something seen outside of their sacred ranks.

"Mortal" bolters are a rank apart and are so designed that mere humans can wield them. Designed with smaller grips and lighter construction, these bolters do not have the same capacity for slaughter as the Astartes versions, yet can easily cut a man in two. Supplied by the Departmento Munitorum to Imperial Guard forces throughout the galaxy, even these pale shadows of Marine bolters are rare trophies to be passed down from generation to generation.

[Cykeisme]

Yes!
I've been looking for canon validation of that fact.

Thank you, Shadowtraveler!

[Connor MacLeod]

So some thoughts even though I’m not familiar with the bolter descriptions myself. Genade launchers like the Mk19 use a high pressure-low pressure system which is rarely used on other types of weapons. I don’t think they’d use it because it would give the shell less space for HE/rocket fuel for its bulk, and unless part of it discard it would also give inferior aerodynamics. Still, it would be possible to use a high pressure-low pressure system in combination with rocket assist if you really wanted.

Probably not for most bolters. Botlers tend to have more in common (if bolters can be said to have ANYTHING in common with a single weapon) with rifles in terms of firing mechanism. From what I read about with the H/L system and grenade launchers, it was done deliberately to get them low muzzle velocities.

Maybe some "normal human" types use them, but I'd bet not.

Giving the advanced technology available it would also be possible to have the projectile have two separate rocket motors separated by a time delay, one launches it out the barrel with a low velocity push, the second one has much higher thrust and gives it long range and hitting power. The most straightforward way to do things though; would simply be to have a small propellant charge launch the projectile and directly ignite rocket motor. Potentially you could also have a duel thrust rocket motor, which it’s basically the same advantage as two separate rocket stages by varying the fuel mixture in a single solid rocket motor casing.

For bolters I'd probably go with the first one with a brief delay built in to allow the bolt to get some distance away before igniting.

All of these methods would produce low recoil, but not no recoil. The low recoil might be to the point that the shear mass of the weapon and its user make it almost irrelevant.

True, but I suspect some bolters (or at least the Space Marine ones) are built deliberately for high recoil, given their power armor (which can also offset any dangers/probelms with exhaust). Others (mainly the human operated ones) probably need less recoil

[Connor MacLeod]

No, all descriptions indicate that it's definitely conventionally fired and then uses RAP to sustain velocity/accelerate to target.

And all bolters have a fairly notable recoil.

Well no, not all. Jaq Draco's bolters are an obvious exception. And hell, I think Eisenhorn's are too (which I should point out presents even GOOFIER bolter nonsense.. namely the "400 kilogram exoskeletonned old witch who was "rigyht on top" of Eisenhorn...)

[weemadando]

No, all descriptions indicate that it's definitely conventionally fired and then uses RAP to sustain velocity/accelerate to target.

And all bolters have a fairly notable recoil.

Well no, not all. Jaq Draco's bolters are an obvious exception. And hell, I think Eisenhorn's are too (which I should point out presents even GOOFIER bolter nonsense.. namely the "400 kilogram exoskeletonned old witch who was "rigyht on top" of Eisenhorn...)

It's not just Draco's bolter, it's also the Squat bolters, the other Inquisitor's bolters and the Astartes bolters...

[Connor MacLeod]

Just on the point of bolter shells: these things are going to be VERY heavy compared to rifle or even shotgun shells.. they pack in both an explosive element as well as the propulsion and all in an armor-piercing casing.

Assuming a ~19mm diameter shell about 2-3" long, and that the thickness of the casing is about 1.5 mm (which is probably conservative, they look alot thicker in the descriptions and probably would need to be I got a minimum casing mass of around 15-20 grams at least, ,assuming iron density.

Further, as the anlaysis before demonstrates, you'd expect at least 10-20 grams of explosive in the shell (even assuming more "advanced" compositions.) for most effects. That will basically double the mass.

And as I said before, there's propellant, and I assumed 10-20 grams of propellant as well.

In the end, at the *bare* minimum a bolter shell seems like it would probably mass at least as much as a .50 BMG round, and probably alot more than that. This is going to be MANY times more massive than most other rounds (even a gyrojet, as large as it was.)

Velocity is another small problem. I previously assumed a velocity comparable to modern pistol rounds, which is optimistic to say the least. Most sources tend to give bolters at least a range of 100-150 meters (DRaco had laspistols that could reach out to 100 meters, and bolters are similarily ranged.. while Angels of Darkness has a Space MArine bolt pistol with a reach of 300-500 metres. Space Wolf implies hundreds of "paces" - at elast 150-200 meters - for a SM bolt pistol.) - that sortt of performance needs, you'd probably need at LEAST rifle like velocities, even in pistol form.

It gets even crazier if you consider momentum. Alot of examples have bolters imparting huge momentum (unexploded) to human bodies.. even in the Inquisition War novels, and that alone tends to reinforce the above. Which is generally why I was so concerned about the "exhaust" issue. Though as I said, Eisenhorn is even worse.

As far as classifying bolters..I generally gave up long ago. THey tend to cross so many classifications its not even funny. They're a horrid bastardization of different weapons concepts: They seem to combine the high rate of fire and ammo storage capability of an automatic/assault rifle, with the explosive qualities of a grenade or small rocket launcher, with the rocket rpopelled capabilities of a RPG or gyrojet or similar weapon. And, top to that off, they seem to have the ammunition versatility of a shotgun (they litterally seem to have a round for EVERYTHING.)

And even then it will still manage to defy descruiptions (mainly due to author fiat about what they think a bolter is) Some use casless ammo, some used cased. Some may do away with either and just be rocket assisted. Some will be a gyrojet (I've seen refrences to that too.) Some may be explosive, or explosive to varying degrees. Some may be purely solid slugs(or behave like it at least.) Some may nto be very explosive, but just vaporize.

Were I to venture a "vague" idea at what might broadly define a bolter, I'd say its a rapid firing weapon using rocket-propelled ammo of some kind that combines explosive effects with a kinetic impact and penetration for damage.

[weemadando]

Up until the 0.75 caliber thing, I'd always been under hte impression that bolter shells were MASSIVE objects, at least in the 30-40mm range given the artwork and some fluff descriptions.

[Connor MacLeod]

No, all descriptions indicate that it's definitely conventionally fired and then uses RAP to sustain velocity/accelerate to target.

And all bolters have a fairly notable recoil.

Well no, not all. Jaq Draco's bolters are an obvious exception. And hell, I think Eisenhorn's are too (which I should point out presents even GOOFIER bolter nonsense.. namely the "400 kilogram exoskeletonned old witch who was "rigyht on top" of Eisenhorn...)

It's not just Draco's bolter, it's also the Squat bolters, the other Inquisitor's bolters and the Astartes bolters...

I'm getting lost here. Jaq's bolter didn't have hardly any recoil to it (it was an explicit quality mentioned in Harlequin as I recall) which tends to differ from alot of other accounts of bolters I can think of.

[Connor MacLeod]

Up until the 0.75 caliber thing, I'd always been under hte impression that bolter shells were MASSIVE objects, at least in the 30-40mm range given the artwork and some fluff descriptions.

Depending on how I calced them, some calcs came out to be 100-200 grams or so (Especially Space Marine bolt shells.) to put that in perspective, thats about the mass of the ammo used in most 20mm cannons (30mm Avenger cannon ammo is something like 300 grams IIRC)

[weemadando]

Draco's was a masterwork bolter of some sort.

I'm referring to the core mechanics of the the projectile with RAP being fired from a cartridge being universal across bolters in Watson's description.

[Zablorg]

Is there a reason why the magazine is so thick compared to the size of the bullets it shoots?

[weemadando]

Is there a reason why the magazine is so thick compared to the size of the bullets it shoots?

That depends, prior to the 0.75 caliber thing it was pretty clear that the shells were that damn wide.

Now, I'd retcon that to mean that it's triple or even quadruple stacked ammo.

[Cykeisme]

Considering the quote by Shadowtraveler on Astartes boltguns being completely different than human-scaled bolters (size-wise), it's possible that 0.75 cal shells are referring purely to bolters for regular people.

Taking into account the quoted description of Astartes bolters, and noting the gigantic magazines (which canonically hold only 20 cartridges), this would logically indicate boltgun shells of commensurate monstrosity.

I can only imagine what kind of shells a two-handed, hip-fired Astartes heavy bolter spits out.

[Sea Skimmer]

Probably not for most bolters. Botlers tend to have more in common (if bolters can be said to have ANYTHING in common with a single weapon) with rifles in terms of firing mechanism. From what I read about with the H/L system and grenade launchers, it was done deliberately to get them low muzzle velocities.

High Pressure-Low Pressure is used to build a very lightweight weapon for the weight of shell fired. It serves to reduce the peak chamber pressure (and thus the thickness of metal needed to prevent barrel bursting) while still allowing for a relatively energetic propellant charge to be used. Low muzzle velocity is a direct result of the need for a lightweight weapon, and is highly variable in any case. The famous M79 ‘blopper’ 40mm grenade launcher for example throws a grenade at barely 75m/s but the Mk19 40mm grenade launcher, which uses the same grenades with higher pressure loading can hit about 270m/s. The first HP/LP weapon to enter service meanwhile, the German PAW-600 anti tank gun, threw its shell at over 500m/s.

[Shadowtraveler]

Considering the quote by Shadowtraveler on Astartes boltguns being completely different than human-scaled bolters (size-wise), it's possible that 0.75 cal shells are referring purely to bolters for regular people.

As a matter of fact, the Dark Heresy rulebook describes "civilian" issue bolters as firing such.