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Can firearm propellant be ignited by piezoelectric crystals that are activated by the trigger? This is for use in a world 50 years into the future similar to Earth. The people there are gearing for war and want to mass produce firearms with as few moving parts as needed without compromising their effectiveness in combat. If you wish, you can even describe mechanisms needed to make these semi- or fully automatic. The mechanism can either be struck by a force or ignited in a similar fashion to a lighter.

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    $\begingroup$ Look into past wars. There were SMGs specifically designed to be cheaply mass produced. Also look into caseless ammunition, using it can simply construction quite a bit. $\endgroup$ – n0rd Mar 29 '18 at 14:51
  • $\begingroup$ As @Catgut pointed that electronically-fired guns are more fragile, you may consider another reason for such solution: protection against seizure by enemy with some kind of biometric authentication. $\endgroup$ – abukaj Mar 29 '18 at 17:44
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    $\begingroup$ Look up "flintlock" :-) $\endgroup$ – jamesqf Mar 29 '18 at 19:08
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The people there are gearing for war and want to mass produce firearms with as few moving parts as needed without compromising their effectiveness in combat.

If the goal is to produce weapons with as few moving parts as needed, piezoelectric ignition is a step backwards.

Electronic ignition has been done before, but specifically piezoelectric ignition implies striking a piezoelectric crystal with a hammer, producing electricity which sets off the round.

There's just one problem with using that electricity to set off modern, smokeless propellant. Firearm propellants are designed to be stable, which is an important part of making them combust at a controlled rate rather than detonating inside the gun, so they are difficult to ignite via electricity or shock by design. This is why primers exist; they produce a quick burst of heat sufficient to ignite the propellant.

So, even for a piezoelectric system, you're going to need a primer. And at that point, instead of designing a firearm to have a firing pin which strikes a piezoelectric crystal which triggers a primer which in turn ignites the propellant, why not simplify the design and omit the piezoelectric crystal entirely?

Note that in the real world, electronically-fired guns do not use piezoelectric systems. The most common form of electronically-fired ammo runs an electric current through a resistor taking the place of primer, and that resistor heating up supplies the thermal energy necessary to ignite the propellant. This requires a power source and onboard control circuitry, both of which dramatically increase the complexity and fragility of a weapon.

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  • $\begingroup$ Presumably the resistor is coated in something (like an e-match), made of magnesium, or some similar boost based on chemical energy. I've used various electrical methods to start fires and none were exactly dramatic (until the accelerant caught -- a paper cup of petrol with steel wool on top, hidden in a bonfire and connected to a car battery by ong leads works well) $\endgroup$ – Chris H Mar 29 '18 at 14:55
  • $\begingroup$ @Catgut You said exactly what I was going to say!! To extend your answer, I would recommend inventing a gun that transfers energy stored in capacitors (becasue they can deliver large amounts of energy super fast) and put that in kinectic energy in bullets. I am not sure if they have done this already, but it is possible. $\endgroup$ – Kavi Vaidya Mar 29 '18 at 19:55
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    $\begingroup$ @KaviVaidya you're describing a railgun $\endgroup$ – Kargathia Mar 29 '18 at 20:40
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It has been done. This chain discusses some of the past experiments: https://www.ar15.com/forums/general/Piezoelectric_Firearms__Primers_/5-1653460/

RPG7 uses a peizo electric primer, and Remington had a peizo electric primed cartridge for its 700 series, but the ammunition was cost prohibitive. http://www.thetruthaboutguns.com/2013/12/chris-dumm/electric-cartridge-primers-gone-but-not-lamented/

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    $\begingroup$ Just to clarify that the piezo part is not in the RPG-7 itself, it's in the warhead. Some of the warheads of the rocket-propelled projectiles use piezo-electric triggers. $\endgroup$ – AlexP Mar 29 '18 at 14:57
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    $\begingroup$ @AlexP Which can lead to some dangerous situations in the case of duds, where you have a half-crushed, extremely sensitive piezo-electric crystal sitting next to the primer in a High Explosive warhead that needs to be disposed of somehow. They can be set off by the shadow of a cloud passing overhead (temperature change). Could be an issue when used in small arms. $\endgroup$ – Wolfgang Mar 29 '18 at 19:40
  • $\begingroup$ Warranty void if dropped. User assumes all liability at point of sale. Ammunition sold separately. State law prohibits the weapon from being kept loaded AT ALL TIMES. Cambering a round without prompt discharge is a felony. $\endgroup$ – Mazura Mar 29 '18 at 23:18
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Your firearm could use an actuator based on the inverse piezoelectric effect, where an applied voltage produces a displacement in a piezoelectric material. Some ink jet printers use this technology to expel drops of ink.

Displacements of a few mm are easily obtainable, with a tradeoff between displacement and impact force.

In this case, the piezoelectric material would move a firing pin which would impact the primer in a typical round of ammunition. The trigger could be replaced by a touch sensor (removing one moving part), and the associated circuitry could produce semi- or full-automatic fire.

The added electronics leave room for lots of interesting wrinkles, like fingerprint ID, double-tap for auto, booby traps in the event of enemy capture. Your list will undoubtedly be longer.

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    $\begingroup$ Double-tap for auto seems like a bad idea to me. I've double-clicked things by accident without meaning to click at all, just by hovering over my touchpad. And if the implementation is sufficiently naive, then the recoil might cause the trigger finger to lose or regain contact, thus creating an unintended double-tap that is accepted as a full-auto command. $\endgroup$ – AaronD Mar 29 '18 at 19:19
  • $\begingroup$ Agreed. Maybe tap and hold, or two fingers. It's doable, in any case. $\endgroup$ – Bandersnatch Mar 29 '18 at 21:26
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mass produce firearms with as few moving parts as needed without compromising their effectiveness in combat

If the goal is to minimize moving parts, what about railguns?

https://science.howstuffworks.com/rail-gun1.htm

Railguns can fire ammunition that is otherwise inert without any moving parts. The loading mechanism should even be able to be replaced with a system similar to the firing mechanism itself at lower power.

However, the more advanced the machine, the less likely field repair becomes. Complexity also usually increases number of things that can fail. That being said, guns are only as reliable as they are due to generations of improvements. If your civilization developed along a different path, railguns may have become the default before traditional guns and a very stable configuration was found.

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  • $\begingroup$ very true, but the only issue is that railguns have extremely dangerous electrical components in which it would be hard to field repair let alone open, coil gun are better in this regard. you'd need a degree in electrical engineering to repair either one... $\endgroup$ – Efialtes Mar 29 '18 at 22:19
  • $\begingroup$ Lookup rail gun on YouTube to see a US Navy prototype in action. A 40 pound aluminum slug travelling at Mach 7 might do a bit of damage when it hits. I'm on my phone so it's hard to look up the url now. $\endgroup$ – pojo-guy Mar 30 '18 at 3:06

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