Absurdly efficient explosives


In Jack Vance’s The Dirdir there was an explosive called “battarache”. Adam Reith’s handgun fired exploding needles. In The Face Lens Larque employed a mining or quarrying explosive called DEXAX in industrial quantities for an imaginative project. There was no particular sign that the explosives were extraordinarily powerful, though you need to get a lot of bang into a small space to make an exploding needle worthwhile.

ForeSight settled on a TL7* explosive called “DEXAX” that was “dangerously unstable” and as dangerous to use as dynamite, but with sixty times the destructive power of TNT. At TL8† it gave us “Plasdex”, developed from DEXAX, and as safe to use as plastique, but only 24 times as destructive as TNT. And for TL9 it offered “Durex”, as safe as plastique or plasdex, but fifty times as bang-o-genic as TNT (I didn’t accept; Flat Black is TL8). At TL8 the “DEXAX needler” and “DEXAX needle rifle” were the civilian pistol and rifle of choice, player characters not caring for spectacular side-effects of laser weapons. I presumed that they were firing something like plasdex, regardless of the name.

DEXAX and its derivatives became part of the texture of Flat Black, like its characteristic weapons and armour, like foam grenades. But I’ve cut ForeSight-isms before, such as the bionic modifications from ForeScene, which used to be standard. I’m prepared to axe DEXAX if it doesn’t carry its own weight in terms of the suspended disbelief.

So: how does DEXAX compare to stuff in GURPS? HEDM rocket fuel has eleven times the energy density of chemical rocket fuel, and is marked TL9, not TL9^. Antimatter-catalysed hydrogen (actually an annihilation fuel, not AM-catalysed fusion fuel) has 144 times the energy density of chemical rocket fuel and is not marked “^”. But when I suggest that DEXAX might be a rocket-fuel derivative having positrons “chelated in molecular Penning traps” GURPS players get very worried about the gamma-rays.

Ought I to keep DEXAX, plasdex, and the DEXAX needle weapons?

* Using the ForeSight scale of tech levels TL7 is the range in which laser smallarms and armoured exoskeletons become practical, the next stage after the Fusion Age. It is an age in which FTL travel is possible only with co-operation at the destination. I map it to GURPS TL9(advanced) and TL10(delayed)

† Using the ForeSight scale of tech levels TL8 is the range in which we get aircars, smartphones, and convenient FTL travel. I map it to GURPS TL10(standard) and TL10(advanced)


Energy density is not the only fruit. Rate of energy release is also important (which maps broadly to detonation wave velocity, which in turn maps closely to brisance). Not that GURPS takes account of this either; it just says that this is an explosive and that is a propellant. (While nobody’s actually done the experiments, the best theories I could find when writing Meltdown and Fallout suggest that “raw” antimatter in air gets you a hot fizzle rather than an explosion. Leidenfrost effect.)

The good stuff at GURPS TL10 is metallic hydrogen, REF 6.

Ted Taylor reckoned the highest possible nuclear weapons efficiency was about 25 TJ/kg, which is about REF 6,000,000; lowest deployed weapons were probably somewhere about the REF 1,000 mark. There is this unfortunate gap between chemical and nuclear, as I discovered when looking into food pills…

Anyway, to return to your actual topic, let’s assume that an Ultra-Tech TL10 25mm explosive bullet is using metallic hydrogen at REF 6, to do its 4d+4 cr ex. If we scale that up to REF 60, damage goes up with square root of REF, so it becomes 6d×3. Or to put it another way, on an unarmoured target, from “about twice your hit points, so you’re probably beginning to be at risk of dying” to “getting close to the auto-death point”.

What that will do to your game is your decision.


In ForeSight a DEXAX needle pistol was damage class 10I, 11I at close range. Tony Purcell’s characters and mine liked heavy reliable models for one extra damage class; whereas DC13 is unlucky, DC12 is rather lucky.

Anyway, DC11 against an unarmoured target: quality rating 1 is an instant kill; QR2 is “critically injured: incapacitated and dying”; QR3 is “incapacitated”; QR4 is a medium wound. And you get one extra wound level on head hits and 20% of torso hits.

This is why I introduced the ‘Reinforcement’ bionic modification. But you didn’t get into gunfights in Flat Black campaigns unless you were willing to kill some people.


So perhaps the question should be, how much does typical armour reduce that?

I’ve spent some time at GURPS TL10 (mostly in Reign of Steel), and there are definitely UT weapons that are optimal for that situation - the Storm Carbine in particular, especially once you can load it with SEFOP.

With this power storage you also get longer-range vehicles, which may or may not be a problem.


At ForeSight TL8 there were basically four types of armour in regular use.

Duty suit was a TL6 product intended for protective work-wear: overalls and what-have-you. At TL8 you could make clothes out of it: formally stiff like suiting material, but inconspicuous except in warm weather. It was radically concealable, light, and did not impede movement at all. Imperial service uniforms were tailored from it, the reason that Imperial offices and habs are air-conditioned to 17°C. The M/I/B protection ratings of dutysuit were A/A/1 and DEXAX needlers were damage class 11 I at close range, so dutysuit reduced their damage from 6/5/4/2 to 5/4/3/1. That is QR1 hits became “critical: incapacitated and dying” instead of “instant kill”, QR2 became “incapacitated” instead of “critical”.QR3 became “heavily wounded” instead of “incapacitated”, and QR4 became “lightly wounded”.

Impermaflex was a TL7 product still used for limb armour and concealable torso protectors at TL8 because it was concealable, not too heavy, and impeded movement little enough that wearers could learn to compensate for it. Imperial Justice Department criminal investigators wore impermaflex vests under their uniform jackets. Protection ratings: 2/3A/2A. Results of a DEXAX pistol at close range reduced to
3/3/2/1, i.e. heavy wound, heavy wound, medium wound, light wound.

Impregnaflex was a TL8 product which demonstrated why you don’t use pistols to fight people in military armour. It was moderately heavy (a full suit with helmet came in at 9 kg), moderately hampering, and completely unconcealable. M/I/B protection was 3A/3AA/5A, which would reduced close-range DEXAX needler hits to MW/MW/LW/stun.

Invulnasuit was the stuff heavy infantry wore on armoured exoskeletons: three times as heavy and twice as hampering, unconcealable and shiny. The gain was mostly in protection against mêlée damage and I didn’t really see the point, but they got a lucky break against DEXAX pistols: M/I/B = 4AA/4AA/5A. That reduces DEXAX needler hits at close range to MW/LW/stun/—, but the heavy DEXAX pistols still got MW/MW/LW/stun.

Dutysuit and the flex/suit distinction across tech levels is part of the texture of Flat Black that I would like to save.

I consider GURPS Ultra-Tech to be a smörgåsbord of alternative technologies that don’t belong all in the same setting. Even if they did all work, some would dominate others in use and make them obsolete. I’ll comb through Ultra-Tech when time comes to write a Flat Black Ezi-Buy Catalogue, but it won’t be my only source and I won’t take all its suggestions.


There’s certainly plenty of Ultra-Tech that doesn’t get much use (gauss weapons, for example, outside very specialised niches are basically outperformed by ETC).

It seems to me that having these pistols means that everyone who gets shot will get fairly wounded much of the time, so it’s closer to the present day military situation (you can have your body armour, but you still need to do something about it when someone opens fire at you) then the standard SF one of being able to ignore small-arms fire. You may even find that people don’t bother to wear armour, because if they get shot they’ll still be badly wounded so they might as well keep the flexibility.


TNT detonation releases about 4.2 MJ/kg. 25 TJ/4.2 MJ ≈ 6 M, so evidently we’re counting REF as approximately proportional to energy density and thinking sadly about brisance, lack of data about.

(I’m not looking too closely at the table on GURPS Basic Set page 415, because it has some entries that don’t seem right: it gives Dynamite a REF below 1 instead of well above, its figure for ANFO seems too low, for octanitrocubane seems too high. But if HEDM rocket fuel is metallic hydrogen then metallic hydrogen’s REF 6 seems about in the ballpark.)

Rocket fuel has a theoretical limit exhaust velocity proportional to the square root of its massic energy, therefore massic energy is in the ballpark of exhaust velocity squared. And delta-V per tank is specific impulse, which is exhaust velocity wearing the false nose of queer units in either case. HEDM has 3.33 times the exhaust velocity of chemical fuels, therefore 11.1 times the massic energy. Rocket fuels are typically a bit more energy-dense than explosives (kerosene-LOX has more than TNT), but that cancels out. The chemical technology that gives us HEDM would seem to offer explosives with REF up to about 10 at TL9.

Following a similar reasoning, antimatter-catalysed hydrogen has Isp about 12 times that of chemical rocket fuel, potentially suggesting REF 144 at TL9.

Likewise, antimatter-boosted hydrogen suggests an REF of 640,000 at TL 10, 5,760,000 at TL 11.

And at the top end, 1:1 suggests a REF 513 million. Jon’s Law!

Now, I don’t fancy handling anything with a REF of thousands, let alone millions. And I tremble at the idea of giving it to PCs. And it looks as though REF 11 is as high as I go without using antimatter. The question becomes

  • is REF 11 HEDX enough to have the sort of texture that REF 60 DEXAX and REF 24 plasdex had in my old campaigns?
  • will DEXAX based on “anti-matter catalysed” rocket fuel but at less than half the theoretical REF pass a sniff test? Or will everyone whine about gamma rays? Say a molecular Penning trap consisted of two iron-56 atoms, 18 carbons, and 18 hydrogen, and chelated an up-down pair of positrons. 346 Daltons, and a Dalton is 1.84×10³ electron masses. One part of antimatter in 318 thousand. One part in 159 thousand conversion of mass to energy (gamma rays), 566 GJ per kilogram. REF 134,000. I can afford to make the molecular Penning traps a lot bigger and pack the actual explosive with gamma-absorbers.
  • Are DEXAX needlers still going to be a thing, with REF 6–11 filling instead of maybe 24? DEXAX needlers had an ammo capacity of 30 in a standard SL pistol format. 9mm pistols go up to 20 rounds double-stacked or ~10 single stacked. I’m going to say needle pistols use single-stacked mags with batteries taking up the extra width of the magazine, because 6mm seems chubby for a “needle”. 3mm × 30mm cylindrical needles offer me 0.21 mL. Call that half explosive. About one eighth the volume of a 9mm cartridge case. With REF 6 metallic hydrogen or REF 11 HEDX we’re looking at 0.75–1.38 times the energy of a 9mm bullet. But we get it as an internal explosion. I think that’s okay.


To me there’s a huge gap between nuclear/antimatter and chemical energies, so I would be dubious about anything actually chemical getting far into double digits.

But, man, if you want REF 60, have REF 60 and say it’s done by molecular-scale gyroscopes or something. Why not?

(Given that internal explosions are a ×3 wounding modifier…)


I’m reluctant to figure out and adopt the implications of molecular-scale gyroscopes, partly because I am trying to hold a line against nanobabble so that my setting be not Drexlerised. I’m not certain that Flat Black needs DEXAX, though I suspect it does. It’s a pity that chemical explosives with REF much larger than 2 seem dubious. I’d need HEDM to get an order of magnitude better than TNT, and that as you say suggests HEDM turbine fuel.


Aren’t molecular gyroscopes still going to be limited by the bond energy of molecules? If you spin them too fast the chemical and intermolecular bonds seem likely to rupture and then the gyroscope flies apart.


“Molecular gyroscopes” is being used as slang for “tech babble”, here.


Maybe that’s how you use it, but Brett sounded as if he were taking the concept seriously. No one tries to figure out the implications of technobabble. Its only implication is “A miracle happens!”


I took the molecular gyroscopes as literal when they appeared in Diamond Age.

And though Flat Black is not hard SF, some of my players are sensitive, so I’m aiming for handwavium only for the enabling devices that I cannot do without, and at least unobtainium for everything else.


I was thinking of them as “not really well understood, but at least plausible-sounding”. And if you have super-strong materials…


Would the Empire would be ok with civilian possession of antimatter?


The Empire isn’t entirely okay with civilian possession of nitrate fertiliser, so…

Practically, a lot is going to depend on how dangerous antimatter is and how vital it is to the economy. I’ve had a PET scan, which technically involved injecting me with a special kind of glucose that produces antimatter, and though the medical staff were hilariously careful not to come near me, to stay the other side of equipment in heavy casings, I was at worst a mild radiation hazard and not a walking WMD. From there you grade continuously up through antimatter-catalysed fusion (safe enough, but confined to reasonably secure power plants) to 200-megaton suitcase bombs, which are only okay if the Navy has them.

The gripping hand is that antimatter is a bit hard-SFy and a bit technothrillerish, and it makes a lot of players antsy even if you explain that you’re only talking about one positron per thousand Daltons of DEXAX. mention it, and you get sidetracked into a physics conversation that kills pace and bores 80% of players. It looks as though I will be able to get the space transport operations I want to make the setting work using fusion and unobtainium. If I can convince myself and prospective players either that Flat Black doesn’t need DEXAX or the DEXAX is achievable, close enough, without antimatter, then i will be happiest not having to mention it. I don’t think that sci-fi readers consider it so obvious a development that its absence has to be explained, the way they do about nanotech and omnipotent matter compilers.


Like many radioactive things, there are trace amounts of antimatter in surprising places, but amounts of it bulky enough to use for boom are deeply worrying. If the Antimatter is being used to make super-explosives it’s more than a mild radiation hazard. A fusion reactor is as you note a secure facility. Sidearm ammo is hard to track, and the main argument I can see for allowing AM catalyzed pistol ammo is that if you can safely extract and concentrate the AM in the ammo, you can also just make it straight up.

This is especially worrying with PCs around.

I’m not a firearms enthusiast, but maybe you could get some mileage from aggressive use of small shaped charges, computer-modulated internal explosions, hyper-velocity, degenerate matter, or good old-fashioned purified beastwastium?

“This is your service pistol. It shoots hyper-velocity degenerate matter explosive needles that do 3d(5) with a linked 1d+2 internal explosion. Don’t shoot anything you don’t want to kill - if you’re lucky it will tear a limb off, if you’re not it will turn everything inside your target’s ribcage into uncooked haggis.”


PCs in Flat Black have so far been pretty good in most cases. Perhaps that’s because I have seldom been one fo the players.

Ooh! Electron-degenerate carbon, like the corestuff of white dwarf stars! 3×10¹⁴ J/kg, very unstable. Do not touch it!

REF 70 million.


“You cannot shoot further than the blast radius.”


Apologies. After some googling I have determined that I have mentally misfiled “Strange Matter,” which is a little less crazy dangerous. We think. Neutronium is not a good thing to mix with civilians, agreed.

As for the original question - Keep explosive needlers, sure, but you don’t need to fill them with AM catalyzed explosives to make them deadly.