Vortex ring projector with incendiary / explosive payload?

[Sam Baughn]

Ultra Tech mentions the possibility of loading a Vortex Ring Projector with 'explosive vapours', but doesn't give rules for this. How would you do it?

I thought that maybe modelling it as a thermobaric warhead could work. A 25mm biochemical warhead would cover the same area as a backpack vortex projector, while a 25mm thermobaric warhead would give 8d cr ex inc, which gives some kind of rough starting point I suppose.

[ronom]

There would need to be a delay, otherwise you're ring ignites at the muzzle.

[Ogo]

Presumably this would mean firing a gasoline or kerosene mist, or maybe a powder of something flammable (heck, flour dust would light up well enough).

Igniting it would be another matter though.

[SuedodeuS]

The point of reference needed is how much stuff is in each vortex shot, rather than how large the affected area is. Unfortunately, while biochemical warheads do give this information, vortex ring projectors do not. I would expect vortex ring projectors to get better efficiency, but covering 2 yards with 1 dose seems a bit much (a biochemical aerosol warhead requires 10 doses to do this). Dropping the dosage requirement 1 level might be appropriate, in which case the 1 yard weapons (pistol and underbarrel) fire 1 dose per shot while the 2 yard weapon (backpack) fires 5 doses per shot. Assuming thermobaric warheads are basically the same as biochemical aerosol warheads, 25mm (8d) is the equivalent of 10 doses, while the 40mm is 40 doses (8dx2) and the 64mm is 150 doses (8dx5). This implies the damage scales as the square root of the fold increase in dosage. So, if 10 doses is 28 damage (average for 8d), 5 doses would be 28*SQRT(0.5)=19.8 (5d+2) and 1 dose would be 28*SQRT(0.1)=8.85 (2d+2). Using grenade costs, thermobaric slurry costs around $1/dose (a TB thimble grenade holds 10 doses and costs $10 more than an HE version; a TB mini grenade holds 40 doses and costs $40 more; a TB hand grenade holds 150 doses and costs $160 more).

As for how this would work, you have two options. Option one is to use a normal mix and fire at/near an open flame for ignition. Option two is to incorporate a small quantity of extra filler that will ignite on exposure to air (within the vortex it can't interact with the air, so it won't ignite until it hits something). Something like powdered sodium (which ignites upon contact with water vapor) might work. If using the second option, range will be diminished (once some of the extra stuff escapes it will ignite the vortex ring) and ricocheting may not be possible. I'd eyeball the new range as about 80% normal and have ricochets drop range by 20% each. For example, the backpack projector (range 30) would have range 24 (round up to 25 to maintain GURPS' pentaphilia), and each ricochet would drop range by 4.8 yards (round up to 5). The slurry ignites at maximum range, rather than simply dissipating. This has the same damage as if it had actually hit something, but it functions as a normal explosive, rather than as a thermobaric (that is, you divide damage by 3 per yard rather than 2 per yard).

So, the thermobaric vortex ring projectors would have the following stats.

Weapon				Damage		Acc	Range
Backpack Vortex Projector	5d+2 cr ex inc	3	25 (-5/ricochet)
Underbarrel Vortex Projector	2d+2 cr ex inc	2	15* (-3/ricochet)
Vortex Pistol			2d+2 cr ex inc	2	12 (-2.4/ricochet)

*this assumes the 20/40 in UT is in error and the intent was 20; rounded down from 16 for easier math

[Sam Baughn]

For ignition, my plan was to couple a VRP to a beam weapon (an under barrel vortex projector on an assault flamer, to be specific).

My intention was to emulate Warhammer 40,000 flamers, which seem capable of acting both like plasma flamers (they project a stream of super-heated gas capable of incinerating people in seconds) and like exceptionally fancy conventional flamethrowers (which can fire around corners, produce explosive fireballs, soak a target in fuel before igniting it and various other tricks).

[SuedodeuS]

VRP's work for gases, not liquids (which you'd need to be able to do things like soak the target prior to ignition). Some sort of aerosolized liquid might work, but you aren't going to be able to soak the target in much of it at a time.

As most WH40k tech is superscience anyway, you could say it's possible to use the fuel as a liquid, in which case it functions just like a flamethrower. In flamethrower mode, the flamer functions exactly like a flamethrower (see HT178-180) with 1/2 the range it has in normal (flamer) mode. It fires in 1 second intervals. Each such "shot" uses a number of shots depending on the flamer used (I'll leave that to you; for example, a hand flamer might use 3 shots of fuel per second, while a heavy would only use 1).