I'm confident in the setting's ability to handle the "logic" as sophisticated as "giant ammo backpacks are for heavy weapons - trying to attach them to other devices leads to stupidity of epic proportions".

Chainsaw swords.

Massed infantry battle formations in warfare with "modern" weaponry.

Spaceships the size of cities.

Cockney orks that make technology work through gestalt belief in them.

Space Wizards being used that have a chance of summoning a literal daemon just by trying to blow out a candle from several yards away.

Bolt guns that fire diamond tipped rocket bullets.

Are we playing the same setting? Isn't "stupidity of epic proportions" kind of the order of the day?

There's "stupid awesome" (basically the stuff 40k is made of) and then there's the usual stupid, like attaching a 15kg charge pack to a 2kg laspistol.

Backpack + combat shotgun = lotsa dakka!

Add a chainknife bayonet for more awesomeness!

I managed to catch a spare moment to post.

From my perspective, I find the multiplicative nature of backpacks illogical while the universal nature of backpacks is even more illogical to (a good number of) others. Small clip weapons exist across the spectrum, from Pistols to Heavy weapons. Even if the backpacks were limited to Heavy weapons, the multiplicative scaling that I disagree with remains.

Chainsaw weapons are already a huge offender of logic (should not instantly warm-up; should require slow, careful application; Strength Bonus should not apply; etc.), yet Dark Heresy supports all these things and more. It would be an overreaction to ban all of these weapons or nuke them into uselessness (e.g., like Meltacutters and their appropriate WS penalty).

Larger clip weapons benefitting more from a Backpack Ammo Supply is an unbiased statement. Saying it is "stupid" to link a Pistol to a backpack is subjective. I "simply" (I use the word lightly) want to treat the objective fact that the Backpack Ammo Supply is biased.

One mental image I always liked is dual-wielding forearm-mounted belt-fed pistols, an image that is supported as written. I do not find that horribly unreasonable for Dark Heresy's setting.

Look, the reload time for pistols is not much of an issue considering it can be done pretty quick. Heavy weapons can take a significant amount of time to reload hence the backpack ammo supply. Plus, one rarely runs out of ammo for pistols considering their low RoF unlike heavy weapons that go through several rounds per trigger pull.

At it's core, the clip size stat represents how big the rounds fired are and how many you can pack in your gun without making it too cumbersome to use - or, in the case of energy weapons, how much "juice" each shot takes and how much you can store without making the weapon too clunky.

If you compare weapons by class (pistol, basic, heavy) and by type (Las, SP, Bolt etc.), you will see these values are more or less consistent. Bolt weapons fire big, bulky rounds, so the bolt pistol can only load a few, whereas a comparably sized SP autopistol can house a lot of relatively small bullets - but at the same time, a boltgun holds a lot more bolts than a bolt pistol, and a heavy bolter even more. A certain variance is then introduced to signify even greater diversity within weapon types - a heavy stubber and an autocannon are both SP weapons, but the former is a machine gun designed for spraying a lot of bullets very fast, whereas the latter is effectively a portable artillery piece, firing humongous, extremely destructive rounds at a much slower pace.

Now, the backpack... obviously, any mechanic that states "take a value from a broad range and multiply it by X" isn't primarily concerned with realism, and will create outliers that make little to no sense.

BUT! Applying the mechanic just to Heavy weapons generally yields results that are intuitively consistent with the differences in caliber between weapons, with smaller caliber weapons having more ammo but all weapons being capable of many rounds of continuous use. The only possible outlier being the rocket launcher, but then again, it's essentially an RPG, and I honestly don't see how you could attach a belt-feeding system to that (this is my general benchmark of "realism" for 40k - if I can't imagine how it would work, it probably shouldn't work).

Granted, the same rule is utter crap when you apply it to other weapon categories, pistols in particular - if a heavy bolter with a backpack supply can house 300 bolt rounds, it's utterly laughable to think a bolt pistol would only house 40 rounds in the same backpack. Then again, why would you use a backpack ammo supply with a pistol weapon? The only advantage of pistols is their relatively small size, which translates to ease of carry and increased concealability, and strapping a 15kg backpack with a semi-elastic feeder belt to the pistol utterly defeats said advantage, leaving you with an extremely clunky setup with greatly decreased range and firepower. If you pack 15 kilos' worth of death in an easily accessible way, you're already dropping all pretenses - you're going to war, so why not put a war-sized weapon on the business end of that loadout? Strapping a giant ammo supply to a sidearm is pretty much equivalent to doing this:

Is that the new standard issue guard knife? Looks good. Now they'll be able to carefully aim for the heart of any orks they face, causing an instant kill. At least according to my Imperial Infantryman's Uplifting Primer.

Is that the new standard issue guard knife? Looks good. Now they'll be able to carefully aim for the heart of any orks they face, causing an instant kill. At least according to my Imperial Infantryman's Uplifting Primer.

Pah! Since orks are extremely cowardly creatures, just the sight of the red laser dot on their chest as you aim for the knife kill will easily rout them! Then you can stab them in the back, the only death xenos filth deserves!

In all seriousness, though, if someone thinks it's cool to strap a backpack ammo supply to a pistol, more power to them, and clearly it should hold many more rounds than the "standard clip times five" indicated. I just don't think it's something the system needs to say explicitly - pretty much all weapon upgrades are handled in one paragraph, and situations where obscene amounts of armaments are required aren't exactly the bread and butter of the clandestine organization like the Inquisition, so I'm fine with them making a rule that works where it's most needed (again, heavy weapons) and that requires a dose of common sense and ST fiat to handle the outliers.

I'd like to point out again that in WH40k pistols have one more advantage which is not negated by adding a backpack power pack:
You can use them one-handed, leaving your second hand free for a melee weapon.

I'd like to point out again that in WH40k pistols have one more advantage which is not negated by adding a backpack power pack:

You can use them one-handed, leaving your second hand free for a melee weapon.

Or you have two pistol weapons that both get hooked up to the backpack and you don't have to worry about how to reload with two weapons in your hand.

Oh, yeah, smart!

I don't know if it's been brought up, because I haven't been through all four pages of the thread, but I could see Backpack ammo work as a multiplier, but only for Las-weapons, and only if the listed "clip size" counts for the weapon is in Charge Packs, even if the weapon specifically only works with Power Packs or Backpack Power Packs.

This would require tweaking the "clip size" for certain weapons, specifically the Hellpistols and Hellguns. This operates on the assumption that a Power Pack or a Backpack Power Pack is equal to a certain number of Charge Packs, and that specific Las-weapons simply use different amounts of the standard Charge Pack charge.

For all other weapons, I have no idea what they were thinking when they made it multiplicative. They should simply be set to a certain size. I have no idea how it's intended to work with certain weapons, though.

I can see how someone is hauling around 200 shots of SP ammo, fair enough, but is it belt-fed from the backpack or something? Flamers, sure, sounds like a tremendous health-hazard, but it's plausible, but belt-feeding from a backpack sounds like some serious machinery that'd at least result in Unreliable.

From a realism standpoint, weapons need to be specially designed for belt-feeding, at which point it doesn't matter that much if you get a larger belt in your backpack or a smaller one attached directly to the weapon.

That's for weapons firing solid, integrated cartridges, of course.

From a realism standpoint, weapons need to be specially designed for belt-feeding, at which point it doesn't matter that much if you get a larger belt in your backpack or a smaller one attached directly to the weapon.

That's for weapons firing solid, integrated cartridges, of course.

Or something.

Because as you say, a weapon not built from a feed would have to be modified to make it work at all (although I can see how some weapons might have double functionality).

Dammit, I'm feeling some houserules coming up...

Also from realism standpoint, the reason you only see belt-feeding on heavy guns IRL is that the self-repeating mechanism is also required to pull the belt further in, where in magazine-loaded weapons the spring in the magazine is used to put the next round where it needs to be. Thus, belt-feeding needs extra energy, and since the self-repeating mechanism takes it's energy from recoil and the pressure generated by the explosion, larger charges are needed to make this work - hence, larger rounds and larger weapons on the whole.

Also, the mechanism needs to be quite sturdy as the ammo belt needs to get broken down with each shot to allow for casing ejection - that means extra bits of metal flying around, so you need a mechanism that can, in a pinch, swallow a few bits that fly the wrong way without jamming. Again, needs bulk to make this happen.

Some mounted guns (such as the famous vulcan minigun) help the process with battery-fed electric motors, but it's not really viable for personal weapons with our current level of technology (the handheld miniguns in Predator and Terminator 2 were real prototypes that never got approved for field use, as they would require about 30 kg extra weight put on the soldier in the form of ammo and batteries - in the movies they were powered by a hidden cable because not even Arnie and Jesse Ventura could really deal with that much crap lumped on them).

Touching upon some of the new perspectives that came up:

I assumed that the Backpack Ammo Supply already implied integrating a belt-feeder mechanism into a gun, otherwise I don't see how a Backpack could accommodate any SP weapons. As was said, Flamers, Las weapons, Plasma weapons and the like could be abstracted to running tubes from the pack to the gun. Characters (players or not) should theoretically be able to modify their weapons to accept belt feeds, but I would say doing so is a one-way trip for most weapons. For Pistols, I would absolutely require the character to take the [Forearm Weapon Mounting] upgrade so the now belt-fed pistols aren't awkwardly cradled in the hands. This more or less makes Heavy-like weapons out of the character's arms.

The [Maglev Impeller] upgrade from <Rogue Trader - Hostile Acquisitions> mentions requiring a non-descript charge pack to function. I imagine that any necessary power source for belt-fed mechanisms is including in the Backpack Ammo Supply upgrade already.

The Backpack Ammo Supply is really just a big mess. Applying logic to the backpack requires applying logic to that logic and makes the whole upgrade more complicated (than it needs to be). I would like to houserule the backpack up for the realism, but the most elegant shortcut that was suggested was the one-time infinite ammo supply.

Ammo backpacks make so little logical sense that they apear to be the imperiums first attempt at replicating ork technology.

Ammo backpacks make so little logical sense that they apear to be the imperiums first attempt at replicating ork technology.

Well, they are a relatively common trope in the kind of fiction 40k draws from, and to my knowledge, there were some attempts to make them happen in real life.

They do make a lot of sense for las weapons - since they're basically battery-powered, carrying a bigger battery on back for either more shots or more powerful shots is pretty intuitive, and since you can transport the charge through a more or less elastic cable, they shouldn't be that cumbersome to use. Ditto for weapons that use "liquid ammo", be it promethium, plasma or whatever melta works on - this actually did work in real life with flamethrowers.

Ammo backpacks make so little logical sense that they apear to be the imperiums first attempt at replicating ork technology.

Well, they are a relatively common trope in the kind of fiction 40k draws from, and to my knowledge, there were some attempts to make them happen in real life.

They do make a lot of sense for las weapons - since they're basically battery-powered, carrying a bigger battery on back for either more shots or more powerful shots is pretty intuitive, and since you can transport the charge through a more or less elastic cable, they shouldn't be that cumbersome to use. Ditto for weapons that use "liquid ammo", be it promethium, plasma or whatever melta works on - this actually did work in real life with flamethrowers.

I want to add that some flame weapons arguably already use backpack-mounted ammo supplies, judging by their descriptions (although I'm unsure if any appear in DH2). But by RAW, there's nothing preventing someone from getting a backpack ammo supply anyway.

In DH isn't there also some weird weapon with a bunch of brains floating in a tank/backpack?

In DH isn't there also some weird weapon with a bunch of brains floating in a tank/backpack?

It was in Radicals Handbook, I believe - four psyker brains in a tank powering some sort of "warp cannon". More heretical than pics of Horus giving Sanguinus a power-wedgie.

Warp canon-Yes yes! Skaven technology is good good! kill many manthings!

Sigh, i want Skaven in 40k.

A bunch of rathead mutants skulking in spacehulks and underhives.

In DH isn't there also some weird weapon with a bunch of brains floating in a tank/backpack?

It was in Radicals Handbook, I believe - four psyker brains in a tank powering some sort of "warp cannon". More heretical than pics of Horus giving Sanguinus a power-wedgie.

That made me think: how about a Warp bomb? (no not a vortex grenade or D-cannon) you take a psykers brain, in a life support jar and chaos runes on it: activate it and the psyker's mind opens a warprift to let daemons in.

In DH isn't there also some weird weapon with a bunch of brains floating in a tank/backpack?

It was in Radicals Handbook, I believe - four psyker brains in a tank powering some sort of "warp cannon". More heretical than pics of Horus giving Sanguinus a power-wedgie.

That made me think: how about a Warp bomb? (no not a vortex grenade or D-cannon) you take a psykers brain, in a life support jar and chaos runes on it: activate it and the psyker's mind opens a warprift to let daemons in.

You'd have to be seriously crazy to ever use it, even as a heretic. Could be fun, though, especially if it caused a roll on the Perils of the Warp table.

The trick to using one is set a timer and be in the next subsector before it goes off