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Basically, 40k is all over the place when it comes to their lasers. Rule of Cool definitely carries the most weight here, I think, between the fluff, the art, the rules and the dozen-plus different interpretations thereof across various media.

Photons technically do have momentum, so they can generate recoil. However it requires such ludicrously huge quantities of energy that for the most part it's insignificant. A 'photon drive' or photon rocket requires 300 megawatts (equivalent to the energy in ~70 kilograms of TNT, but energy is not necesarily explosive power. Also easily equal to the energy content of several gallons of gasoline or diesel.) So for any laser weapon to have 'recoil' based on photons and anything close to even a low end rifle woudl require many hundreds, if not thousands, of megawatts.

That is more than enough energy to cremate a human-sized body in short order (melta and plasma gun level firepower, basically) so that doesn't seem likely for a lasgun (if it does explosive damage as the fluff indicates, you don't want to how how ludicrously powerful this translates to. It still wouldn't apply because it would certainly be outdoing bolters.)

Note that the laser rifle will still have recoil in a technical sense at lower outputs, its just going to be such an infinitesimal impulse it might as well be recoilless. (300 Mw for one newton of thrust per second.. if we say a 10 kj laser 'shot' would be about .033 millinewtons/sec - one thousandths of a newton - or 33 micronewtons/sec. A 9mm handgun might put out around ~4-5 newton-seconds of recoil as a very rough approximation.)

Now the shot will have insignificant recoil, but depending on how the lasweapon is designed, it might generate recoil in other ways. Power generation or beam generation might involve some sort of chemical or other explosive reaction not unlike gunpowder there are devices that could produce electricity via chemical reactions like a flux compression gneerator and you might have recoil that way (although not neccesarily significant.) Similarly, any sort of cooling system may involve venting or ejecting gases or similar (open cycle cooling) and that may or may not generate recoil.

If you wanted your laser to have recoil, I'd say the 'chem powered' approach is more likely - it would have advantages over supercapacitors or batteries in terms of energy density and releasing it (batteries suck at discharging energy rapidly, and even supercapacitors don't store it nearly as well as batteries do.) Besides, a raygun powered by chemical reactions (like most IG weapons in principle) seems like it would just fit into the setting.

Raven911 wrote:
Thats what I would think, but In one of the GG novels it mentions the sniper adjusting for windage, which shouldn't be a problem with a laser beam. I guess its just creative license with the writers.

How about a plasma gun?

Is the Sniper a laser based one?

IIRC Space marines use solid shot or needle shot iirc while i think guardsmans can vary but can be supped up lasguns.

Aren't there Sniper Rifles in universe that use a invisible laser to propel a poisoned needle? The laser's to pierce armor, and the needle- well...it's poisoned, right?

That could be why he's adjusting for windage and all- in order to make sure the needle hits the target instead of veering off to the side.

The Needlers (the laser + poison sniper rifles) use magnetic induction to hurl the poison sliver since a chemical propellent would cause the toxins to melt prematurely. Coilguns don't have much recoil either.

From someone who uses lasers to assist with long distance shooting:

Lasers have not nil but insignificant recoil.

But recoil also has nothing to do with windage nor elevation.

Windage is adjusted when either (a) you want to account for wind - which wouldn't really affect a laser, or (b) you want to account for lateral movement of a target - i.e. a vehicle moving at a fixed velocity, but given the speed of light, this shouldn't be a factor either unless we are talking starship speed.

Elevation is adjusted when either (a) you want to account for Gravity - which wouldn't really affect a laser unless we're talking about the magnitude of a black hole which can bend light, or (b) you want to account for a non infinite point of intersection when your scope is mounted at some height above the barrel - i.e. not exactly in line with the barrel, but if you don't care about an exact intersection and just align scope and barrel in parallel, you should just be 2 or 3 inches off at all ranges.

TLDR, should really not have to adjust Windage nor Elevation for Lasers.

The Ghosts novels and Abnett about the time of Honour Guard started changing how the Ghosts were depicted and how stuff was handled (the .50/.30 cal support weapons show up, platoons became smaller and more numerous, flamers and rocket launchers were more widespread, everyone had tube charges, etc.) and lasweapons generally became 'lazer bullet shooters' and had recoil, windage/elevation stuff (with the sniper rifles yeah, which were still long las) and it even got to the point where it took lasfire a second or so to cross a mere hundreds of metres. Which I kinda get as a stylistic/atmosphere choice but it is still kinda silly to novelize STar Wars blasters. Doesn't matter to me much cuz I still enjoy the novels.

The first three books lasguns were definitely lasers and there was other stuff (EG ghosts had meltaguns back then too!)

Lasers will have atmosphere issues, but its mostly focused on a.) burning through atmoshpere, and b.) focusing laser energy down to a small enough point at effective ranges (especially for pulse lasers.. heat rays less so.) It is possible windage/elevation stuff has something to do with the optics or adjusting the laser for focusing for some reason, but I could be talking out my rear/speculating wildly in that regard.

Connor MacLeod wrote:
The Ghosts novels and Abnett about the time of Honour Guard started changing how the Ghosts were depicted and how stuff was handled (the .50/.30 cal support weapons show up, platoons became smaller and more numerous, flamers and rocket launchers were more widespread, everyone had tube charges, etc.) and lasweapons generally became 'lazer bullet shooters' and had recoil, windage/elevation stuff (with the sniper rifles yeah, which were still long las) and it even got to the point where it took lasfire a second or so to cross a mere hundreds of metres. Which I kinda get as a stylistic/atmosphere choice but it is still kinda silly to novelize STar Wars blasters. Doesn't matter to me much cuz I still enjoy the novels.

The first three books lasguns were definitely lasers and there was other stuff (EG ghosts had meltaguns back then too!)

Lasers will have atmosphere issues, but its mostly focused on a.) burning through atmoshpere, and b.) focusing laser energy down to a small enough point at effective ranges (especially for pulse lasers.. heat rays less so.) It is possible windage/elevation stuff has something to do with the optics or adjusting the laser for focusing for some reason, but I could be talking out my rear/speculating wildly in that regard.

Correct focus is definitely a thing that needs to be accounted for with lasers. Especially with atmospheric effects. Depending on the laser, if it diffused as much as 1/60 of a degree, it would be 10 inches in diameter at 1000 yards. But one would never call it an adjustment of Elevation or Windage.

This applies too to other weaponized "laser like" systems including Ion weapons, Particle Beams, etc. Their mass is too small and their speed too fast to need Elevation or Windage correction. Unless we are talking Starships.

The only way to rationalize it is that there's some sort of projectile with non insignificant mass being conveyed by the laser somehow.

Plasma would need W/E correction but it wouldn't be confused with lasers.

Oh well, makes for more interesting reads in any case.

The beam itself might not produce recoil, but the weapon itself could have recoil. It might forcefully cycle air with each shot to aid in cooling, or it might just be an odd artifact of the way it is made. Like maybe it has recoil compensators that mess up it's design.

With IG fluff, almost anything goes because of how varied everything is.

I always thought that a Lasgun produced a "bullet" of superheated matter/gas rather than a laser beam, however short that beam might be. That's why they do not instantaneously (or as good as at rifle ranges) connect with the target. I always thought it was as if the powerpack produces a laser, which creates and then propels a chunk of superheated plasma (though hugely less powerful than a plasma gun).

Something else I've never really understood, along with recoil depending on writer, is do lasguns make noise when they fire?
If yes/no, why?

Yes they would make noise. A slight cracking noise from air displacement.

Even current medical/industrial lasers make a static like crackle when working.

As far as lasers generating recoil, we are currently testing a laser based thruster system(with the added benefit that there may be evidence of a warpbubble being created in the resonation chamber via far less power output than was originally thought necessary to create one), so obviously a laser can produce a significant amount of directional force depending on the inner workings.

Since the primary energy transfer from gun to target is heat/light rather than kinetic impact, the recoil isn't a significant feature of the lasgun even if there is some felt. With a slugthrower you're feeling the backblast of the force that was used to launch the bullet, dampened by the weight of the gun and spread out against your shoulder by the stock. With a lasgun, the recoil energy is a mild byproduct of the beam or bolt being projected and doesn't come anywhere near the force you're putting towards the target.

Lasguns despite the power pack may operate as Chemical lasers (maybe the power source operates as an initiator, or its a variation of a lasgun type. Hotshot power packs may involve a non-renewable source of power like a chemical laser to allow higher performance and such.) I'm not aware of any actual chemical lasers that DO have recoil, mind, but we don't have true laser weapons and any sort of exothermic reaction should have the possibility (especially if confined) fo generating recoil (not to mention having to dispose of the byproducts probably, so you might even have 'gunsmoke' or 'muzzle flash' of a sort given the right reaction) but you could probably handwave something to have a lasgun with recoil (doesn't have to recoil as much as a slugthrower though.) Alternately the recoil may be due to some mechanical part of the process (why, again is totally beyond me, but you could have it.)

Beyond that you have to go the route where lasguns fired some actual bullet or bullet like stuff at 'less than c' velocities and somehow contained or emitted photons. Having lasgun as a particle beam weapon would also potentially permit recoil of a sort (you would still probably need a laser as part of the process to create a 'path' to keep the particle beam focused and hopefully minimize any nasty side effects (radiation sickness is a potential hazard concern of any 'realistic' particle beam weapon.) This would incidentally ALSO explain the visible beam and Ghosts lasguns of the later series are blue anyhow IIRC. (it wouldn't be unprecedented either. Andy Chambers described lances in BFG as some sort of particle beam/laser weapon hybrid too as I recall.)

 Kommissar Kel wrote:
As far as lasers generating recoil, we are currently testing a laser based thruster system(with the added benefit that there may be evidence of a warpbubble being created in the resonation chamber via far less power output than was originally thought necessary to create one), so obviously a laser can produce a significant amount of directional force depending on the inner workings.

You're talking about the EM drive? There's some extreme disagreement over what that actually is, and the majority of people whose opinions I trust on legitimately scientific matters are skeptical, despite the whole 'NASA' angle. Science is not totally bereft of personal or politicla/economic/etc. motivations, and tons of internet articles on technology tend to be full of hype. Especially of stuff like this nature (remember the 'FTL neutrino' stuff not too long ago?)

That said I don't think its actually a laser anyhow. Stuff can involve EM radiation without being lasers, and even if it was doing that it probably has nothign to do with lasgun recoil. In fact, generating more force for LESS energy would be a rather poor weapons design, since recoil negatively impacts accuracy and other performance.

The em drive interferometer experiments did specifically use lasers, or at least the test prototype that may have generated a warp bubble did. The experiment will be reproduced basically in my backyard (Cleveland Ohio)

It was in the laser resonation chamber that the warp bubble was (possibly) observed.

I have been looking into ideas on possible real-world ftl travel for something i am writing; which is what lead me to the nasa article on the possibility that we could have it much sooner than we ever expected(subject to verification of the possible observation of course, and then followed by discovery of an application)

 Kommissar Kel wrote:
Yes they would make noise. A slight cracking noise from air displacement.

Even current medical/industrial lasers make a static like crackle when working.

Thanks! That's a much nicer visual than just silent fire fights.

Heh, even if lasguns were completely silent, there's still the whoosh of flamers, rat-ta-ta of stubbers and whistle-thud of mortars to contend with... not to mean the screams of the injured, praying of the fearful and bellowing of assault elements.

That's even before you factor in the fact so many alien noises. Wailing Doom Scythe engines, the damned whistling over the blades of a Reaper Jetbike, the zzzzzzap! of Ork heavy weapons...

.... the Chk-Whrrrr of Assholetep's eye.

 AegisGrimm wrote:
I always thought that a Lasgun produced a "bullet" of superheated matter/gas rather than a laser beam, however short that beam might be. That's why they do not instantaneously (or as good as at rifle ranges) connect with the target. I always thought it was as if the powerpack produces a laser, which creates and then propels a chunk of superheated plasma (though hugely less powerful than a plasma gun).

No, it does create a beam rather than "laser bullet" like Star Wars. But it's not like a Star Trek Phaser either which you can see moving. It would be more like a beam that goes completely from the gun to the target. Probably can't even be seen from most angles. That's probably a more realistic take on a laser gun than either SW or ST. It is travelling at the speed of light after all.

 Furyou Miko wrote:
Coilguns don't have much recoil either.

Why not? They're accelerating a bullet-like mass away from you at high velocity. It really isn't very different to a standard gun in terms of force.

 Frozen Ocean wrote:

 Furyou Miko wrote:
Coilguns don't have much recoil either.

Why not? They're accelerating a bullet-like mass away from you at high velocity. It really isn't very different to a standard gun in terms of force.

Indeed. Rail and coil guns have a lot of recoil. They're accelerating objects with substantial mass.

Which is why the Tau must have incredible mastery over kinetic energy in order to be able to mount huge railguns not only on skimmer tanks, but actual aircraft.

The Skimmers are the impressive bit. Aircraft aren't a huge deal. The A-10 exists after all, and the GAU-Avenger has some serious recoil.

 Psienesis wrote:
.... the Chk-Whrrrr of Assholetep's eye.

And the POWPOWPOW of boltguns.

And the schwmmmmmBZAAAAAP of Wraithcannons.

40k is noisy.

I always imagined Wraithcannons as being "brrrrrrWHOOOMP"

DoWII's Wraithcannons have it down for me.

https://www.youtube.com/watch?v=ZysJC4EQEKo

 Grey Templar wrote:
The Skimmers are the impressive bit. Aircraft aren't a huge deal. The A-10 exists after all, and the GAU-Avenger has some serious recoil.

True, but look at the size of the guns in relation to the aircraft they are attached to! Treating them as having essentially negligible recoil is still impressive. But you are right, it is more impressive on a Hammerhead.

EDIT: I keep imagining a Valkyrie with vanquisher cannons.

The GAU-Avenger's recoil actually causes the plane to slow down. But it still works just fine. I doubt the railguns are much of a problem for something that's traveling at similar speeds.

The Hammerhead probably has recoil dampeners, or extra anti-grav to counter the recoil.

Frozen - the Punisher Vulture is a thing

 Furyou Miko wrote:
Frozen - the Punisher Vulture is a thing

I know (I have the guns, and a Valkyrie waiting for them!), although it's not really a GAU-8 equivalent (the punishers are much too small for that, they're more like standard miniguns). I meant in the sense of an Imperial equivalent to the AX-10 Tigershark; a plane with two absolutely enormous (relative to the craft), high-powered cannons on it. Come to think of it, that sounds definitely Ork.