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I am working on a concept for a low velocity rail pistol that would fire taser integrated rounds. Kinda like these shotgun slugs.

Could I use the rails to simultaneously fire and charge the round?

To clarify, I'm thinking of a sci-fi civilian weapon. I know I tagged reality check. But I was curious where the technology gaps would be. It looks like energy storage is the big hurdle.

If better energy storage was assumed, is there another obstacle?

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  • $\begingroup$ Is there a reason you wanted it to be a rail gun? From what I understand of the technology the region of velocities you are targeting is better handled with chemical weapons. Rail guns tend to gain popularity as you start to try for velocities higher than conventional explosives can reach. $\endgroup$
    – Cort Ammon
    Commented Nov 23, 2015 at 0:53
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    $\begingroup$ I would like it to be quiet. Also I like the idea that the speed of the projectile could be controlled by the gun to give it more versatility combined with alternate type of rounds. $\endgroup$
    – Night_Fox
    Commented Nov 23, 2015 at 0:59
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    $\begingroup$ For quiet weapon, airgun or a spring-loaded gun (or even a coilgun) will be vastly easier to achieve. Railguns - even small ones - require enormous capacitor "backend"; they really only make sense with extreme velocities because they don't scale down with energy nearly as gracefully as alternatives. $\endgroup$
    – SF.
    Commented Nov 23, 2015 at 13:23

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Given the state of material science, I'm afraid you're out of luck.

Clearly, you envision the payload energy being stored in a capacitor which is charged by the rail voltage, but you haven't looked closely at just how much energy is required. The PopSci article suggests an output voltage of 500 volts at 1.3 mA for 20 seconds. The energy required is then $$E = V i t = 500 \times .0013 \times 20 = 13 \text{ Joules}$$ Assuming the capacitor is charged to 500 volts during launch, $$E =\frac{CV^2}{2} = 13$$ and $$C = \frac{2\times E}{V^2} = \frac{26}{250000} = ~100 \text{uF}$$ and since this would produce a capacitor which is completely discharged (no voltage) at the end of the 20 seconds, a factor of 10 should be applied, for a final value of 1000 uF at 500 volts. Such a capacitor does in fact exist, but it's much larger (40 mm dia x 105 mm long) than the taser round (18.5 mm dia x ~75 mm long). Worse, the capacitor alone weighs 170 g compared to a total taser projectile weight of 25 grams. Figuring a final projectile weight in the vicinity of 250 g, a one-handed launcher (pistol) would probably break your wrist.

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  • $\begingroup$ Well I think that's a great answer. $\endgroup$
    – XenoDwarf
    Commented Nov 23, 2015 at 13:16
  • $\begingroup$ Greatly appreciate your answer WhatRoughBeast. It's nice to get intelligent answers to what may be a ridiculous question (without all the hate). Where else could you ask question like this? $\endgroup$
    – Night_Fox
    Commented Nov 24, 2015 at 23:09
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Probably, but there is no point. If you want it to be non-lethal, which seems likely for a "taser-bullet" you want the velocity and energy of the bullet to be relatively low. So you can just use a piston driven by a linear motor to accelerate the bullet. You'd want a system for recovering the energy used to drive the piston and reload the gun, which would add complexity and mass.

But seriously, propellants are generally better for storing and releasing energy than batteries, so you'll probably need a major battery technology breakthrough before this makes sense. Currently using a bullet driven by conventional propellant and charging it with piezo- or pyroelectric effect is probably more effective.

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  • $\begingroup$ See my answer for why your charging methods should be reconsidered. $\endgroup$
    – WhatRoughBeast
    Commented Nov 23, 2015 at 2:35
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    $\begingroup$ @WhatRoughBeast I already read your answer. I am not actually assuming capacitor based storage, just answering the question about using the rails to propel and charge by pointing there is better solution for either. So the issue with capacitor density is not really relevant to me. But since you commented: Since the charge storage on the bullet is only used once and for a very short time, its characteristics would be entirely different from those of a capacitor designed to be used reliably for years. Honestly I'd go for something that generates the voltage on or after impact myself. No storage. $\endgroup$
    – Ville Niemi
    Commented Nov 23, 2015 at 2:49

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