Shuriken Operating Characterisics

[Nabterayl]

Greetings, ladies and gents! I'm running a 40K roleplaying game (adapting the rules of another system, which is why I'm putting this here and not in the Dark Heresy forum), and the mechanics of the game have caused me to ask a question: how much recoil do shuriken weapons have? I turn to you, fellow lore hounds, for help.

My first instinctive answer was "None, because of space elf magic." And I suppose that s always a valid supposition. But shuriken weapons are described as using an "impulse" to propel their ammunition down the firing tube (slot?), which certainly implies recoil. And, perhaps most challenging to the no-recoil view, according to IA11 dire avengers prefer to fire single shots despite having 100 rounds in each magazine. That could be because dire avengers are poncy gits who can't be bothered with the inelegance of automatic fire, but it's evocatively consistent with the behavior of soldiers armed with automatic rifles, who virtually never use automatic fire because it's less precise - if only just, with a good weapon and good technique - than firing the same number of single aimed shots. This suggests to me that shuriken catapults are not literally recoilless, though Bladestorm suggests that a well-trained eldar shooter can handle the recoil of 1500 rpm and still hit things.

So I'm currently leaning towards "enough recoil to be felt, but not a lot." Alternative views? Agreement?

[Wolfshade]

Lets work it out!

What do we need?

Law of conservation of momentum.

Excellent.

Before shooting the momentum, p = 0.

After shooting the total momentum p = 0.

After shooting p = m1v1 + m2v2,
where m1 is the mass of the shuriken v1 is the muzzle velocity and m2 is the mass of the shuriken pistol and v2 is how quickly it would recoil.

Now we know that the muzzle velocity is very quick and the shuriken is very light, and the mass of the shuriken pistol >>> shurkien.

I think the issue will be a very small recoil enough to be felt but not a lot.

Also given that the shuriken would spin then the pistol will be rotated in the opposite direction, again with negligable effect.

[energongoodie]

Lets work it out!

What do we need?

Law of conservation of momentum.

Excellent.

Before shooting the momentum, p = 0.

After shooting the total momentum p = 0.

After shooting p = m1v1 + m2v2,
where m1 is the mass of the shuriken v1 is the muzzle velocity and m2 is the mass of the shuriken pistol and v2 is how quickly it would recoil.

Now we know that the muzzle velocity is very quick and the shuriken is very light, and the mass of the shuriken pistol >>> shurkien.

I think the issue will be a very small recoil enough to be felt but not a lot.

Also given that the shuriken would spin then the pistol will be rotated in the opposite direction, again with negligable effect.


BOOM!
Knowledge bomb dropped. Awesome! :)

-_-

[DrLove42]

Thing you need to remember is recoil is a direct reaction of Newtons law.

Every action has an equal and opposite reaction.

The force required to fire a monomolecular blade is likely very small (after all it doesn't require much force to accelerate such a low mass object).

Therefore the force applied back to the gun is tiny. And the gun (and indirectly the holder) is much larger, suggesting to me next to nothing in terms of recoil

[bfmusashi]

Space Elf Magic wins. They generate and manipulate gravity on a whim and the swooping hawk backpacks show they can miniaturize these devices. Keep in mind, it's a space ninja gun made from solid emotion... it mocks math with the power of heart.

[Nabterayl]

I've never bought the notion that shuriken are "monomolecular" in the sense that they are one molecule thick everywhere on the disk. One molecule thick on the edge, perhaps, but the disk itself seems like it must be convex (literally convex, not necessarily to the naked eye). Otherwise how do we explain the fact that a catapult only carries 100 disks, or the fact that Bladestorm literally expends the ammo cylinder, when paired with the large and conspicuous spare cylinders carried by dire avengers?

And then there are the ballistics characteristics of a literally one molecule-thin disk. Seems like it would be liable to snap on impact - if it ever got to impact, as its incredibly low momentum would mean even the Brownian motion of inert air would push it around. And how would Mkoll see the thing stuck in a tree and be able to pick it up with his bare hands?

So, at least for purposes of this campaign, I'm not willing to accept shuriken disks that thin. In the mass range of a few grams is my working estimate - on the same ballpark as a small bullet.

Leaving the physics aside for a moment, is anybody aware of any behavioral or textual evidence that hasn't been brought up? The IA11 passage about semi-auto fire and the fact that you can't get more than 3 hits out of Bladestorm suggest to me that there is some felt recoil. What about in other works, such as the eldar Path books (which I have not read)?

[Gotthammer]

Space Elf Magic wins.. it mocks math with the power of heart.

Ma-Ti would have been a lot more tolerable if he had a shuriken catapult instead of a monkey.


I don't recall much mention of the specifics of shuriken weapons in the path books, but I do remember an old bit of flash fiction where a pair of harlequins shoot up a genestealer describing the gun jolting.

[Anggul]

IA books are rarely a good fluff reference. They're composed mostly of Imperium-jerk and not even accurate Imperium-jerk at that.

The whole 'not just spraying shots everywhere' thing is just sensible, dexterous warfare. Why spray and waste ammunition when you're good enough to pick off your enemies with precise, well-aimed bursts?

[Nabterayl]

I like IA personally, because they don't try to write mythology. Aside from Dan Abnett, IA is the only Black Library source I know that consistently tries to take 40K seriously (I might add that of the four times the Imperium has gone up against xenos in IA, it's gotten its *ss kicked three times). But even if you don't like IA11's depiction of shuriken catapults, do you have an alternate source to suggest that a catapult magazine holds more than 100 disks' worth of matter?

The problem I have with "short, precise bursts" is that people don't fight that way even now, with automatic rifles whose recoil is eminently controllable. Talk to any of the servicemen or servicewomen in your life, or look around on the Internet for the experiences of combat veterans, and the picture quickly emerges that pretty much only machine gunners use automatic fire, and even then mostly for suppressive (that is, psychological) effect (my sincere apologies if you are a serviceman with a different view of automatic fire; the foregoing is based on the experiences of the infantry veterans and other servicemen in my life).

Now, I'll be the first to crown the eldar kings of the needlessly complicated route to the desire result game, even in a universe full to bursting with needlessly complicated routes to the desired result. Ordinarily I would have no problem with eldar shooting a guy 100 times to achieve the same effect as a single bullet (it would hardly be the least efficient weapon in their arsenal even so). But I'm inclined to think that eldar really would object to even short, precise bursts unless their weapons had significantly less recoil than ours do, because they would find it artless (and the shuriken catapult, we know, holds a special place in eldar culture as an art form).

Which is why I'm interested in the recoil. If we have good documentary evidence of eldar using short precise bursts, I think that would argue for very little recoil. But all the evidence I'm aware of either directly states that shuriken weapons have recoil (per Gotthammer), or indirectly indicates it (e.g., Bladestorm, IA11, FFG).

[DrLove42]

Black Library , the Path series. Talks about troops spraying the enemy. It talks of Space Marines dying with hundreds of shurikens embedded in their armour is seconds.

Also i distrust the fluff in IA11. A Wraithseer is killed by a Rune Priest. Thats a T8 4W creature being killed by a S3 attack. Wolf bikers survive being sucked into the warp by Wraithguard guns. Nightwings, the best aircraft and pilots in the universe make a 1:1 kill to death raio. The seers dont see an event as massive as the detonation of a huge area of land exploding before hand

So no, i dont trust the fluff in IA11 one bit

[Wolfshade]

This question has been bugging me for a little while so I got my pen and paper out and decided to sort it out.

[---! Warning Dangerous Assumptions Ahead !---]

A shuriken catapult has a range of 12" (or at least the effective range). Using the converstion that marines are 7 feet and their models are 28mm we end up with a real life effective range of 232m.

If we assume that this means that the "bullet drop" will be less than 12" based on hitting a human torso and how far off you can be and still be lethal.

Also, we'll assume that air resistance is negligable, that is because the effect of bullet drop would be more pronounced then air resistance, also it makes the maths easier. Also assuming that we are shooting at about 1G.

Regardless of how fast the muzzle speed we can calculated the time taken to drop by 6".

s = ut + 0.5*a*t^2

Considering verticle movement:

s = 0.3048m (12" in m), u = 0m/s, a = 9.8m/s^2, t = the unknown we want.

working it out we have t = 0.25s

Now we can consider the horizontal movement:

s = 232m (our effective range), u = the unknown we want, muzzle velocity, a = 0m/s based on our assumption, t = 0.25s

working this out we have a muzzle velocity of 930m/s the same as a M-16. If we assume that the M-16 is the same mass as the Shuriken Catapult then we have a mass of about 4kg. If we assume that the shuriken is 1g (a massive over estimate given they are supposed to be mono-molecular, our equivalents are 12g)

Now using conservation of momentum:

0 = m1v1 + m2v2

m1 = 0.001kg (mass of shuriken), v1 = 930m/s, m2 = 4kg (mass of catapult), v2 = the unknown we want.


Working it out we get a recoil speed of 0.23 m/s, this is about a quarter of the recoil impulse from a .40 S&W or 9mm luger.

Now in reality, things will be a little different, I have no idea of the actual weight of the catapult and how on earth in 40k ranges are defined. As has been said above, if the disks are mono-molecular thick then their deviation would be quite extreme because of skin friction so the air desnity would be quite pronounced. Similiarly we have no idea of the mass of the disks either and that is a big contibutor. The only way I could see that figure changing is them to be much lighter, after all some sources cite that you can get 1000 in a clip, that being the case an assumption of 1g would give the clip a weight of 1kg which while not massive, is enough if you have it in an out stretched arms. All these would decrease the recoil.

[Nabterayl]

DrLove - thanks, that's helpful. In the scene you describe, how many shooters are we talking about? Even if there are "hundreds" of disks in the space marines in "seconds," number of shooters is important to infer the firing behavior described.

Wolfshade - what sources describe 1000 rounds in the magazine? That's certainly interesting to hear.

[Wolfshade]

It says here http://warhammer40k.wikia.com/wiki/Shuriken_Weapons though doesn't cite it's sources :( but given they are described as mono-molecular thick it means that you have an obscene amount in just a 1cm clip.

[Xenith]

Ever considered that the 2shots, AP5, S4 is just an analogue of the guns ability to kill a marine? An 18 shot, S1, AP- basic weapon on a 10 man squad of guardians is not feasible.

A shuriken weapon kills the opponent through the death of a thousand cuts, for heavily armoured opponents, it's hoped that one of these cuts will be somewhere important.

I'd imagine the recoil would be somewhere in the realm of a cellphone/PS3 controller vibrating. The Eldar codexes describe them as effectively recoilless.



Look to inquisitor.

[Nabterayl]

"Monomolecular" doesn't have to mean "one molecule thick." As long as the edge of a blade has been honed to a single molecule's thickness, the blade is monomolecular. Nobody images monomolecular swords as being one molecule thick throughout the blade, do they? I don't think we can infer anything about mass from that word. An edged weapon could have the mass of an entire solar system, be a light-year thick at its thickest point, and still be monomolecular if it was big enough.

I certainly have considered that a single S4 shot could represent multiple disks. That suggests to me, though, that the recoil on a shuriken catapult is considerable (and by "considerable" I mean "about as much as an M4," which of course is quite controllable). Normal shooting for a catapult, whatever that means in terms of actual rounds per minute or round per trigger pull, gets you a minimum of 14 S4 shots in a single magazine. Going rock and roll and emptying the magazine gets you ... 3 S4 shots. And you can't even get any S4 shots that way without specialized training.

Why would this be? I can think of two reasons:
Game balance.
The recoil of a shuriken catapult is significant enough that blowing through your entire magazine in a second or two (which the gun is mechanically capable of doing) significantly degrades your accuracy per shot compared to whatever normal firing behavior is.
Because the point of this exercise, as well as my personal style as a DM, is to hold universes fairly tightly to the implications of their lore, I reject #1. That leaves me with #2, so far.

Of course, #2 is still compatible with enormous magazines and "normal" firing behavior being the discharge of multiple disks. #2 could mean that mags are about 100 disks and normal firing behavior is semi-automatic; it could also mean that mags are 100,000,000,000,000 disks and normal firing behavior is short bursts of 100,000,000,000 disks.

EDIT: Every game system I'm aware of indicates that shuriken catapult mags are roughly 100 disks. Even Inquisitor, which is a pretty high-resolution system (and written by the author of the Path series), would have us believe that they have 80 disks' worth of matter in the mag, and have about as much recoil as any other weapon.

EDIT 2: To preempt one possible objection to 100ish round capacity, I can still think of good reasons to have a solid ammunition block even if it merely gets you an incredibly large (instead of ludicrously large) number of shots. The weight savings would be significant, and the weight efficiency also very significant, if you didn't have to spend mass on the magazine, propellant, or casings. Even caseless bullets spend a significant amount of the magazine's weight on the magazine itself and propellant. In an eldar-style ammo block, every gram of the "magazines" you schlep ends up downrange.

[Eberk]

Well, I'm not smart enough to calculate how much recoil there will be and I don't have a lot of background info about magazine content, etc...

What I would like to add to the discussion is 'gut feeling' ;)

Eldar are not very tough but that doesn't mean they are weak and will break whenever someone touches them. I consider them ... (don't know the correct english word for looking frail but being more tough than it would seem).

They are also more advanced than mere humans, so no explosives to propel solid iron balls used in their weapons.

Monomolecular... yeah, look at razor blades but than sharper (the edge of the razor blade is thinner then the rest, otherwise we wouldn't be able to use it I think... it would just break)

Single shot weapons ? No, I think about 'small bursts' of shurikens (5 or 10 in a 'shot'). Off course this doesn't mean they 'spray' a location with shurikens, they can shoot good enough to make them all count. It seems to me that bolts from a boltgun (which explode inside their target !) will be as lethal as say +/-7 shurikens embedded in you body. 1 single shuriken just doesn't seem to have the same killing potential as for example a bolt from a boltgun.


So, what does all this 'gut feeling' leads me to...

To a weapon that fires short bursts of projectiles with a bit of a recoil but not enough to 'hurt' or discomfort an Eldar when he shoots.


As said before... I don't have sources to support my thinking and I don't have formulas to validate my claims... it just 'feels' like how Shuriken weapons should work.
(Sorry if I bored anybody or didn't contribute to this thread)

[Nabterayl]

Gut feeling is important too. It's fine to make the style choice to write a book or run a game that is more "serious" than most 40K literature, but it still has to feel like a version of 40K or why bother?

[bfmusashi]

While I disagree with the idea the catapult suffers from recoil the Dire Avenger's ability to empty the magazine while a Guardian can not is further supported by the difference between aspect armor and the mesh guardians wear. Aspect armor is rigid when the wearer doesn't want it to move as it is psycho reactive (at least it was in the 2nd ed codex). The guardian mesh is simply armor. Recoil is implied and I think in the Fantasy Flight games you still have to brace the shuriken cannons to avoid a to hit penalty... so recoil is reflected in the game.

[Anggul]

Fantasy Flight are even less reliable than IA. Mesh armour becomes rigid upon impact, it doesn't stabilise their firing stance in any way. The recoil is negligible and Eldar are really good at what they do. The reason Dire Avengers are more accurate is that they're more skilled. Also, I'm not sure what the general understanding of 'short precise bursts' is, but it certainly isn't spraying into the enemy. It's letting off a minimal number of rounds but still enough to cause damage. Of course against Space Marines they'll let loose because the heavy armour necessitates it, but most things in the galaxy won't be wearing power armour, so it's unnecessary. Each shuriken can slice through flesh and bone with ease as stated in the codex, but when it comes to heavy armour you've got to fire more shots to increase the chances of hitting weak points.

Also Shuriken Catapults used to be the same as Storm Bolters.

In 3rd ed their range was suddenly reduced to 12", and no-one was sure why because it made them rubbish. The 18" range Dire Avengers got in 4th ed was lovely, but still left Guardians rubbish. Now that rapid-fire weapons can fire at full range on the move, even the 18" range Avenger Catapults are poor. They need to give Guardians 18" range and Avengers 24" range again.

[Nabterayl]

Anggul, your deprecation of Inquisitor and FFG suggests that you view catapult ammunition blocks as being good for more than 100 shots, and that you subscribe to the ~5 shot burst view of normal firing behavior. Why is that? Do you have sources to adduce, or is it just your gut feeling?

[Wildeybeast]

Ma-Ti would have been a lot more tolerable if he had a shuriken catapult instead of a monkey.

Beat me to it. Still, I think this sums it up.


http://3.bp.blogspot.com/_YltWwb0i8fQ/TD9w5dfY9gI/AAAAAAAAApI/pDy-X420Lo0/s1600/Captain+Planet+-+Heart+2+COL+copy.gif

[Wolfshade]

Trying to work out maths based on game fluff and gut feelings do not do well for your sanity.

[bfmusashi]

I didn't claim mesh armor dealt with recoil, but aspect armor does. It becomes rigid when not being intentionally moved by the wearer. I only brought them up as shuriken cannons are treated as heavy weapons for the purpose of reducing accuracy.
And in Heart's defense, you could use it to sick orcas and tigers on dudes. Ma-ti was just lame.

[Alan Connell]

The question id ask is how do the catapults fire the discs, as that would determine the type of recoil, for example a chemical propellant will be more powerful in recoil as its a controlled explosion, however, what happens if its done using superconducters and mag lev technology, where basically the ammo isnt actually touching anything in the fireing chamber and is propelled forward with a pulse of magnetism (much like the bullet trains in japan.

just my 2cents to try to approach from a different angle.

[Wolfshade]

The force of the recoil isn't effected by launch method. Momentum must be conserved.
Though where the recoil is experienced might not be the opposite end of the muzzle.

https://www.utexas.edu/research/cem/IEEE/PR%2052%20Weldon%20Publications.pdf

[Alan Connell]

The force of the recoil isn't effected by launch method. Momentum must be conserved.
Though where the recoil is experienced might not be the opposite end of the muzzle.

https://www.utexas.edu/research/cem/IEEE/PR%2052%20Weldon%20Publications.pdf

excellent link. though then my next possible and far out of the park idea, which we will call "go to sleep and stop drinking coffee by the bucket load idea" or could come under the now trademarked "space elf magic" theory of maybe the projectile is fed into a miniture webway portal and exits where the muzzle is, that would surely give no recoil, could also allow for 100`s of shurikens to pepper the target in a burst of one trigger pull, thus causeing the afore mentioned death by a thousand cuts method. :)

[Alan Connell]

http://wh40k.lexicanum.com/wiki/Shuriken#.UR2LVGcl_mw according to lexicanum they are based around gravitic accelerator similar to land speeders propulsion systems.

hope that helps somewhat.

[AM-254]

They are monomolecular disks, thats disks that are a molecule thick on its edges. Assuming the shurikens aren't made of some bulky polymer, that means that the discs are very light and have next to no air resistance. Thus even at when propelled at great spead by a mechanism, I would imagine that there would be virtually no recoil. The Eldar have had a long time to perfect the arts of war.

[-Tom-]

Various good replies already in this thread, covering conservation of momentum among other things. However, also bear in mind impulse - how quickly is momentum changing. If you fire a bullet, in a flintlock pistol (as a very simple firearm example) the bullet is given it's maximum velocity at the moment of ignition of the gunpowder - the equal and opposite force is therefore experience as one 'snap' of recoil. Automatic weapons can 'channel' some of that recoil force into a means of loading the next round into the chamber, which reduces the recoil felt, although they are still working in the same way of giving the bullet maximum velocity instantaneously. If, instead, you imagine a shuriken catapult to be an accelerator (magnetic, or electrostatic for example), it will be applying a more constant force while the ammunition travels down the barrel getting faster as it goes. In this case, the reaction force or the recoil would not be so instantaneous and would feel relatively 'weaker' at any moment in time.

For the issue of the nature/shape of the ammo, I think would be best to think about a samurai sword. These were made to be very thin along the front edge, and were cooled in water to make the metal form into small crystals to enable them to be made very sharp, while the back edge was kept warmer so larger, stronger, crystals formed. Let's assume therefore that a shuriken has a thin edge for sharpness, and thicker core for strength and also to give it more mass (because that mass is a factor in the momentum the ammo has, same as the velocity is, which is important in how much damage it will do - consider A-10 Thunderbolts which use depleted Uranium bullets for tank-busting).

Saying 'mono-molecular' doesn't really tell you that much without knowing the shape and size of the molecule... a water molecule looks a lot different to a molecule of ascorbic acid. As far as the fluff goes, this is really just saying that Eldar are happy to use nano-technology to make bullets. I suppose ideally, you'd have some sort of molecule that was largely made of carbon atoms arranged in a similar formation to diamond for hardness but with much heavier atoms in the thicker core for added mass... probably something like depleted Uranium. You'd also have the nice side effect of being able to electrostatically charge the carbon as a means of accelerating it down the barrel.

As for accounts of how much ammo, I think the idea that there are only 100 shurikens in that clip is maybe too few, but maybe it is a case of semantics. If it were the case that the catapults fired bursts, like some semi-automatics do now, you might consider that you have 100 shots, of 10 shuriken bursts, which would sort of work with both the 'ammo stock of 100' fluff, and the 'targets peppered with 100's of shurikens' fluff...?

[Nabterayl]

I'd like to thank everybody for their replies in this thread. While I'd welcome additional discussion, I thought I should give folks an update. I've decided to go with 100-disc cylinders for now, and enough recoil to be mechanically relevant but much less recoil than any other weapons in the game. Without going too much into system-specific details, a shuriken catapult can be fired in a 3-round burst with no more recoil than a single shot, but more than that (up to a maximum of 15 per attack action for regular catapults, and 25 for Avenger catapults) begins to degrade the accuracy of each trigger squeeze - again, not by too much, especially compared to other weapons, but enough that it starts to affect your dice rolls. One of the things I need to worry about in this system is how the weapon would behave for a PC who acquires a shuriken catapult but has no training in its use, so these little details become important even if, say, a Dire Avenger would have enough training to make it functionally irrelevant in most cases (even a Dire Avenger who empties his magazine in a single round is going to have his accuracy significantly degraded, though he should still score a few dozen hits - but I think the fluff is fairly consistent that even Dire Avengers don't do that except in very select circumstances).

That may not be a perfect representation of the (imperfect) fluff, but I am running a game, and I think this will still give the players shuriken weapons with the right "look and feel," which of course is the ultimate goal.

[-Tom-]

but I think the fluff is fairly consistent that even Dire Avengers don't do that except in very select circumstances).

That may not be a perfect representation of the (imperfect) fluff, but I am running a game, and I think this will still give the players shuriken weapons with the right "look and feel," which of course is the ultimate goal.

Fluff and fair game mechanics most likely will never go hand-in-hand anyway... let's face it, fluff-wise for the technology they are supposed to have the Eldar ought to turn up to battle completely invisible due to holo-fields, kill everyone with barely missing a single shot due to advanced targeting systems, make some snide comments about the inferiority of their opponents architecture and pop off back into the webway before anyone even knew they were there. However, this wouldn't make for a very fair game.

Good luck with the project!