40K lasgun analysis methodology thread

[Connor MacLeod]

It looks like the one to three megajoule range is the most recurring number, with 600kj and 7 mj outliers. Would it be reasonable to use that range when referencing your calcs?

In my mind I tend to go with the 1-3 MJ for "standard" shots (or "low power" if you go with just the high/low setting type of lasgun.) I suppose it could be a bit higher or lower depending on how many settings you figure on and how conservative you want to be.

One reason why I tend to figure on 1-3 MJ is that las-pistols tend to be "high kilojoule" - ie triple digit kilojoule to low megajoule (single digit)
While I know the games tend to rate lasguns and laspistols as similar in power/damage, I tend to regard this as pure game mechanics (hellguns do the same damage too, yet we know they are considered more powerful weapons.) I generally figure that, like real life guns, the rifle variant (assault rfile) will be at least several (2-3) times more powerful than the pistol variant (M-16 vs 9mm handgun, for example)

Calcs "generally" tend to support this. In general I'd say "max power" settings tend to be at least 8-12 MJ for a lasgun.

But again thats my opinion

Looks like. Fortunately, discrepancies can be smoothed out as most lasguns have settings. Some three settings, some two, some more elaborate ones seem to have a variable slider. So anything between one to six (or indeed, nineteen, if one want's to call 'megathules' megajoules) seems possible.

Yep. There are probably "heavier" lasguns (that heavy infantry like the jantine and Volpone use) as well as lighter ones (like the compact carbines)

There could be other reasons for variations. Due to limiting barrel damage, its also possible that maximum 'per shot" output can differ depending on rate of fire (full auto may do less "per shot" damage than single shot, yet do more damage overall, for example.)

Another likely possibility is that different power packs may have different "per shot" yields. We know there are different kinds fo hot shots (some offer "20' shots per pack like the ones used in long-las, wheras later Gaunt's Ghosts novels have hotshot packs that are good for one shot only before being used up.) and we know standard power packs can differ in ammo supply, so differing in damage capacity isn't all that great a leap either.

As far as "megathule" goes I tend to look at that as more of a "sustained" output, but it could just measure a sufficiently powerful 'maximum output" burst. Going by the "uplifting primer", "19 megathule" seems to reference the magazine type as well as something else.

[Connor MacLeod]

Ooops, new post. I decided to toss in another quote. I was gonna save this until I covered the Gaunt's Ghosts novels since it was partt of the omnibus, but its a nice couple of quotes and I feel lazy (and want to show off for finding it.)

The founding omnibus, page 760

The flickering of the daylight was being caused by bright las-roudns passing over us, almost invisible against the hard glare of the sky. Then a shot stung by against the bricks and I saw it clearly. A dart of seething fire, tinged red, the size of a man's middle finger, so bright it hurt my eyes, so fast it was barely there.

Las-beams appear to be "finger" thick, which implies a diameter of a few centimeters. By itself its not hugely useful (except for hinting at beam intensities) but it does help with some calcs I can do later on.

Page 763

But Mktag had been shot. Right there in front of me. He fell at my feet, his heels drumming the ground, his hands spasming. A tiny plume of smoke spiraled up from the little black hole a las-round had made in his forehead. There was no blood. The shot had cauterised the entry wound and it didn't have enough power to exit his skull. Its heat and force had been expended getting into his cranium and incinerating his brain.

It was quite simply the most awful thing I have ever seen. His body thrashing, trying to live, the brain extinguished. I think if there had been more blood, more obvious physical damage, I could have coped better.

But it was just such a tiny hole.

Las-round "incinerating" a human brain. I've calced it already, but out of curiosity (and to see whether anyone can figure it out themselves) I'll hold back on the yield for now (or explaining it.) See if someone can come up with a figure close to my own (I bet a few of you could.)

[Falkenhayn]

That's a very odd report of damage, the Mktag incident. I don't think I've ever read an accounting of a similar wound. Gory/Cauterized crater, showered viscera, decapitation, all appear much more frequently.

[Shroom Man 777]

Could be explained by the las round being weak? Just scorched a tiny hole and impared heat, giving the guy a stroke of some kind?

[NecronLord]

The laspistol excecutions Shasam metes out to various tyranids in Xenology seem to be similar, poke a neat hole into the head...

[Falkenhayn]

The laspistol excecutions Shasam metes out to various tyranids in Xenology seem to be similar, poke a neat hole into the head...

Strange.

I'll yield to Xenology, though the fact that its against a 'nid and not a Human concerns me some.

[Connor MacLeod]

You tend to see those types of wounds show up alot more frequently in the later Ghosts novels, and there are IIRC some others unofficially. Most typically they're tossed out by idiot anti-40K fanboys who are trying to claim lasguns really aren't as powerful as calc'ed. There are other examples of "non explosive" - the most immediate are a case where some guy gets his face cauterized in the first Gaunt's ghost novel, and later when Feygor gets shot in the throat (again cauterised, but evidently lacking explosive effects.) Ther'es also a bit in the Inquisition War when a astropath gets her brain boiled without her head exploding (though that IS a laspistol..)
There are also more than a few incidents where las-fire hits metal things like doors (Ghostmaker and Guns of Tanith most immediately come to mind) and they drill holes straight through, not explode. There's also Medea in Eisenhorn (Who gets shot by a las and has the wound cauterized, but does not suffer a massive gaping crater in her chest.) And IIRC Ghostmaker they punch through thighs (and water) in a straight line - agian non, explosive.

Additionally, more than a couple "cutting lasbeam" incidents (again the Ghosts novels and Inquisition war) are also non-explosive.

This isn't neccesarily "inconsistent" with the ability to cause "explosive" damage (exploding heads, chests, blowing off limbs, exploding hearts etc.) Its simply a matter of how the energy is delivered, which is a function of the design or configuration of the gun (ie: different settings)

As noted before, to cause the "explosive" effects you h ave to deposit a large amount of energy (preferrably concentrated on a small area) VERY rapidly, in order to quickly (and violently) vaporize a section of the target and create an explosive-like shock wave (supersonic or higher propogation.) Those sorts of effects are going to be very rapid (probably far faster than the eye could notice).

The "non explosive" effects on the other hand probably last for a second or less (more probably a quarter second or so.) - much "longer" than the detonation time of an explosive, ,typically. So your effects won't be quite as "violent" either.

Now that I think about it, its possible the "non explosive" setting is more thermal than the "explosive" one on the basis of power/wattage. If total energy is held constant for "explosive" and "non explosive" settings, the strain on the gun could be greater for the "explosive" setting because the gun has to handle that energy in a much shorter timeframe than the "non explosive" setting, which could conceivably strain the barrel.

As an extention, its also possible the "explosive" settings tend to be less effective at cauterizing, which may also explain why in some cases wounds sitll bleed (although the concussive effects can trigger secondary bleeding even after cauterization too.)

Given that, we can probably conclude that in addition to "rate of fire" adjustment settings and output/charge settings (low or high yield), there is probably "explosive" and "non-explosive" settings (and possibly "hybrid" ones as well.. why not.) Although of course some lasguns probably aren't nearly that versatile (hotshots seem to be invariably set on "explosive, high powered, non sustained" shots, for example.)

[Connor MacLeod]

That aside, noone has any ideas on the yield? I'm kinda disappointed, I thought I might have explained things well enough that it could be calced, given how I've discussed incineration and head/brain wounds in the past.)

[Connor MacLeod]

ah well. Noone seems to want to answer my question, so I'll tell you. Incinerating (IE reducing to ashes) a Brain (which for an adult male masses in at around 1.4 kg average) would require around 3-5 megajoules or so to incinerate completely. If we just assumed "cauterization" temperature (call it 300-400C) would be 1.3 to 1.8 megajoules. In theory you probably would get at least some incineration with cremation level temps, but it wouldn't be complete.

[Connor MacLeod]

Finally decided to do a bit of an update here... addressing specific issues with lasgun not related to firepower...

For some time now the whole "lasgun rate of fire" issue has bugged me a bit. A few of you may remember having tangled iwth me in the past over the issue, most notably the
"apparently" slow rate of fire of lasguns - 220 rpm, in the "Uplifting primer". In the past, I've cited examples of lasguns having higher rates of fire: either draining powerpacks rapidly (the Cain novels) or specific rates of fire in other novels (Crimson Tears., 13th Legion, Grey Knights, etc.) I operated under the assumption that a lasgun needed to behave like a projectile weapon (Despite knowing they're not the same)

Boy, was I stupid.

There was, if I'd actually given the issue some thought, some very good reasons why lasguns need not be "high" ROF weapons, and why a low "apparent" rate of fire does not matter. The simple answer is: Lasguns fire sustained beams, and such beams are demonstrably visible to the observer in firing. Human reaction times are about 1/4 of a second average - there is some evidence 40K humans *have* significantly higher reflexes (Traitor's Hand and Eye of Terror both hint at humans having reflexes potentially as fast as 1/10th of a second, though whether this is typical or exceptional isn't known - and it does point ot some measure of "better" reactions than RL humans even if it is exceptional.) so we might fudge the ROF issue some there, but its still not likely to be a whole lot faster than 5-6 shots/sec in most cases.

There is, however, another aspect of lasers vs bullets that makes high rates of fire unneccessary. Lasguns can fire as a sustained beam (notable examples are First and only and the Inquisition War novels, but also the Ben Counter ones.). In those modes they generally act like some sort of cutting/slicing weapon, and this has the benefit of being able to "sweep" multiuple targets or hordes of enemies quite easily and mimicking a "full auto" burst. With the slow ROF, the ability to "slice" or "Rake" with even a single shot would be improved (duration is long enough for the eye to track)

This leads us to an interesting conundrum. We have the "high ROF" guns I naturally mention above, and there is other evidence (mainly Inquisitor, Dark Heresy, etc.) which suggest most lasguns are not fully automatic but "semi-automatic" (which is the 40K term for burst fire.)]

There are a number of possible answers for this:

- The higher-ROF models are "rare" variants or specially-produced models alone. We have examples of "specialist" variants like the long las, assault las, ,and so on and so forth. It does not seem difficult to imagine that

As a corroborating fact we do know that some RL assault rifles have been converted into a sort of LMG/SAW, and in the case of a lasgun it ought to be easier.

- Lasgun “bolts” are composed of a series of individual “bursts” - in other words, each “beam' is a series of pulses giving the impression of a continuous beam (or, may be a continuous beam – it
doesnt really matter for our purposes either way.)

This last bit would expalain the “assault las” kage uses in “Last chancers”, as well as other seeming inconsistencies. It is worth noting real life lasers can/do use “pulsed-beams” (this helps allow vapourised material albated from the surface to dissipate between “shots”) - it might also allow for “wider” damage despite the fact some lasguns make small holes in the target.

Then again, both possibilites could be true as well. Lasguns are diverse enough that there could be both kinds in existence.

Then there's the M-G short pattern (Uplifting primer) versus the Mars Pattern (mentioned in both Inquisitor and Dark Heresy, mainyl) Both have appeared in other novels (Ben Counter and Abnett's come to mind most immediately) These may or may not be the same weapons (the M-G is also apparently known as the “M-Galaxy” pattern.) but they're implied to be far more common than “other” patterns, evne though the M-G pattern is “single and fully automatic” and the Mars pattern fires in “single and Semi-automatic (or burst)”) This may be either representing variants, or two different kinds of wepaons, but obth for different kinds of “regiments”. The M-G pattern might be issued when ammo wasting is a concern (primitive regiments, penal regiments, etc.) while the Mars pattern is issued to more “professionaly” trained troops. A real life comparison might be AK-47s vs M-16s.


(PS if you wonder why I link “semi” with “burst” its worth noting that the 3rd Edition rules and the Imperial Armour boooks indicate that bolters fire off several bolts per trigger pull, and in Inquisitor/Dark Heresy they are almost universally semi-automatic and single shot, like lasguns, thus I assume the meaning is similar. Nevermind, of course, that “semi” and “full” auto would be roughly the same number of shots, making such distinctions meaningless as well...)

anyhow, that should resolve that

[Nyrath]

There is a handy-dandy back-of-the-envelope online calculator for the effect of a given laser beam on selected materials, available here:

http://panoptesv.com/SciFi/DamageAverage.html

[Connor MacLeod]

HAh.. he updated the site. Thanks, that's quite useful. It'll also prove useful if I have to deal with some idiot again who assumes that "x amount of energy equals the effects of y amount of TNT"

[Connor MacLeod]

I've been tooling around a bit and thought of another potential way to calc some incidents from older materials I'd covered. I was going to put it in the individual threads but that seemed excessive since I'm kinda necroing as it is, but this works since I've necroed this one in the past.

First one is from 13th Legion:

I pull off my helmet and look at it, still a bit dazed from the hit. There's a charred gouge just where my right ear would be, almost burnt through. I poke at it with my finger and I'm shocked when my fingertip passes straight through. The las-bolt had been within the thickness of a piece of parchment from actually getting through!"

And this one for Ghostmaker.

The laser burst punched through the top of the bandit's bowl-helmet, presneted as it was by his head-down appraoch. The shot probably passed down through his skull, his neck, and his torso, following the line of his spinal column, Merrt thought, as the figure dropped stone dead in a crumpled pile.

Back when I did the Uplifting primer analysis, I noted the following about Guard helmets:

The helmet you were issued with will provide you with the best protection avaialble. It is lightweight (about 2 kg) and extremely durable. It is fully capable of deflecting las-rounds, slower velocity solid shot and shrapnel. It is built using several layers of carbon-fibre and contains the earpiece of the vox-link. When activated this powerful receiver will pick up orders and information from the squad or command centre vox-com.

By calcing it using the properties of carbon (a rough but reasonable approximation) we can calc the amount of energy needed to nearly burn through the helmet.

We know lasguns vaporize explosively on impact (at least along the length of passage and close within the diameter of the beam). We know the diameter of a lasbeam from previous sources is roughly finger thick (13th Legion itself, backed up by the Ghosts Short story found in "The Founding" omnibus, as well as other novels like Ravenor and Dawn of War.) We can conclude that a lasgun beam's diameter is about 2 cm, and thsu the hole probalby is. It is possible on the context of the quote the "patch" is bigger, say ear size (maybe 5 cm diameter?) - this may be due to explosive vaporization, motion of Kage's head "spreading" the shot around, or superconducting properties of the helmet. I'll go with ~3 cm simply to be conservative. For a larger estimate it could be doubled.

Assuming the helmet resembles a Cadian pattern helmet as depicted in various sources (a reasonable approximation) we can assume roughly an inch or so thickness at ear levle (maybe 2 inches from some patterns/diagreams, but that simply would double the calc and need not be separately calceed.) I'd say half that is a more conservative estimate, especially for the head.

Density of Carbon is ~2260 kg*m^3 Melting point is ~3800K Boiling point is 5100K (300K starting temp assumed) Specific heat is 710 J/per kg*K This means that at room temp (300K) it takes 2.5 MJ per kg to raise 1 kg of carbon to the melting point and 3.41 MJ/kg to raise it to boiling point.

Heat of fusion is 8.72 MJ/kg (at least by Enthalpy) Latent heat of evaporation is goign to be ~30 MJ per kg by "heat of vaporization" and 60 MJ by "enthalpy of vaporization" (which I take to be the same thing, but go figure.

Overall, call it 30-40 MJ low end and if it turns out to be higher or the higher figures are actual, so much the better. It still works out as an Order of magnitude anyhow.

note: (all properties for Carbon pulled from here

for a 3 cm thick, 3 cm diamter "hole" through the helmet, the mass affected would be on the order of .05 kg (fifty grams or so). Given the energy values above we can conclude it would involve at least 1-2 MJ (at least) to burn a hole through a helmet. Like I said, that's conservative, and it could be higher (inefficiencies, for example) but as an OoM calc it works to verify the mutli-mj outputs Lasguns can achieve per shot.