Emerging smokepowder weapons in my fantasy

[Icelander]

One PC is receiving a set of magical pocket pistols in a 'deringer' style, made out of orichalum with double barrels 3" long. The grip of one of pistol is made from shark's tooth and the grip of the other from mother of pearl. The former pistol is decorated with engravings of the PC defeating divine emissaries of their enemies and defending his men from sharks in the ocean and the other pistol has him fighting beside sahuagin (shark men) against the nobles, priests and generals of the other side.

The weapons carry various enchantments, but the ones I'd like to get help with are the ones that ignite the smokepowder and are meant to get the most of the propellant in a short barrel.

Pulling the trigger activates an Essential Air spell to fill the barrel with the essence of oxygen and ensure rapid burning of the propellant and simultaneously causes the 3 FP version of the Ignite Fire spell to go off in the entire barrel, the equivalent of a blowtorch being applied to the 25 grains of finely-ground REF 0.8 smokepowder (about mid-way in REF between high-quality black powder and TL6 smokeless powder). A Shape Air spell ensures optimum mixing of the burning propallant and the Essential Air while the combustion is going on.

This propels a 10mm 90 grain lead and antinomy ball out the barrel. The orichalum construction means that there is no risk of catastrophic overpressure despite the near instant detonation of the smokepowder. I figure that it could use a larger powder charge, but as it's so tiny and the grip only allows three fingers, we want to avoid too much of a kick.

I can use Doug Cole's spreadsheet to find the stats, but I need to know what would be reasonable in terms of PSI, burn length and, derived from that, the muzzle velocity.

What would be a reasonable figure for muzzle velocity? 1,200 fps? 1,500 fps? 2,000 fps? 3,000 fps?

[johndallman]

1,200 fps at most. That's the velocity of a .45 Long Colt black powder cartridge, which has Rcl 4 in a much larger and probably heavier handgun, according to High-Tech p94. Trying to use more power than that in a tiny gun is likely to result in it flying out of the user's hand.

[Icelander]

Originally Posted by johndallman

1,200 fps at most. That's the velocity of a .45 Long Colt black powder cartridge, which has Rcl 4 in a much larger and probably heavier handgun, according to High-Tech p94. Trying to use more power than that in a tiny gun is likely to result in it flying out of the user's hand.

Even if this thing had double the velocity of the .45 Long Colt, it would still have much less momentum and therefore less recoil impulse. It's a 90 grain ball vs. 230 to 255 grain one.

The .45 Long Colt is also black powder, whereas this is using magical smokepowder which has 60% more REF for its volume. Black powder revolvers are not particularly efficient, wasting propellant energy because the cylinder seal is not perfect. As the barrel of the magical 'deringer' is a smoothbore orichalum tube with no moving parts or any need for a seal (it's a muzzle loader where the charge is ignited magically), ideally, almost all the energy generated should go toward accelerating the ball

And with Essential Air, Shape Air and Ignite Fire, the entire charge should ignite nearly instantly and with very high efficiency, accelerating the projectile to a much higher velocity than REF 0.5 black powder would.

I'm looking to benchmark quite how fast. I'm leaning toward anywhere from 1,500-2,000 fps.

If it got 1,600 fps, the recoil impulse would be about equivalent to standard pressure 9x19mm Parabellum ammunition.

[scc]

Originally Posted by Icelander

One PC is receiving a set of magical pocket pistols in a 'deringer' style, made out of orichalum with double barrels 3" long. The grip of one of pistol is made from shark's tooth and the grip of the other from mother of pearl. The former pistol is decorated with engravings of the PC defeating divine emissaries of their enemies and defending his men from sharks in the ocean and the other pistol has him fighting beside sahuagin (shark men) against the nobles, priests and generals of the other side.

The weapons carry various enchantments, but the ones I'd like to get help with are the ones that ignite the smokepowder and are meant to get the most of the propellant in a short barrel.

Pulling the trigger activates an Essential Air spell to fill the barrel with the essence of oxygen and ensure rapid burning of the propellant and simultaneously causes the 3 FP version of the Ignite Fire spell to go off in the entire barrel, the equivalent of a blowtorch being applied to the 25 grains of finely-ground REF 0.8 smokepowder (about mid-way in REF between high-quality black powder and TL6 smokeless powder). A Shape Air spell ensures optimum mixing of the burning propallant and the Essential Air while the combustion is going on.

This propels a 10mm 90 grain lead and antinomy ball out the barrel. The orichalum construction means that there is no risk of catastrophic overpressure despite the near instant detonation of the smokepowder. I figure that it could use a larger powder charge, but as it's so tiny and the grip only allows three fingers, we want to avoid too much of a kick.

I can use Doug Cole's spreadsheet to find the stats, but I need to know what would be reasonable in terms of PSI, burn length and, derived from that, the muzzle velocity.

What would be a reasonable figure for muzzle velocity? 1,200 fps? 1,500 fps? 2,000 fps? 3,000 fps?

Too complicated for a start, and if I was GMing I'd say that the Ignite Fire results in the barrel heating up, dropping your rate of fire. Really what you want is Fast Fire cast on the ammo.

[Icelander]

Originally Posted by scc

Too complicated for a start, and if I was GMing I'd say that the Ignite Fire results in the barrel heating up, dropping your rate of fire. Really what you want is Fast Fire cast on the ammo.

Of course the barrel heats up, but it takes three times as much to heat up an orichalum barrel than a bronze one. Note that the Ignite Fire is effectively cast by the magical item in question and doesn't heat up the item itself any more than a wizard casting Ignite Fire has his fingers burnt. But obviously, the combustion of the smokepowder heats the barrel as normal.

Not that firing often enough in a minute for that to matter is likely to come up with a holdout gun like this. The PC probably can't even manage more than 8-10 shots in a minute, even with succesful Fast-Draw (Ammo) rolls and no Aiming. I can't really imagine a situation where he'd fire often enough to overheat an orichalum barrel with magical protections.

In any case, the only danger would be ammunition cook-off. The PC is immune to fire and the orichalum weapon is Fireproof, Shatterproof and Soilproof.

Fast-Fire smokepowder is a good idea, of course. Maybe not the basic load, but definately specialised ammo.