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The Question

How would a gun, that uses anti-gravity as propellant, work? Is it even practical?

Background

I have been toying around with the idea of a gun that uses anti-gravity to shoot off heavy, non-magnetic materials as bullets. The weapon itself is costly, high-tech gear. However, this society has managed to mass produce it to fit their tactical doctrine.

Since its non-magnetic, magnetic 'deflectors' can't bounce it off.

The weapon uses a miniature 'variable gravity' generator, and a small reactor to power it. It's a (By comparison to most weapons.) Heavy weapon, (8-12 Kg range.) It does not jam, (uses the generator to pull bullets towards chamber.)

It basically shift the paradigm of warfare from 'defensive' to 'offensive' since enemies can't rely on magnetic shields, and heavy plate.

Clarification

Is it, in the given conditions, practical? If yes, then would it work the way I think it will? 'IE; anti-gravity pushes bullet out really quick.' or would it just push everything out.

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    $\begingroup$ "Folks, we need to stop using our heavy antigrav weapons for hunting and celebrating and shooting at the Moon. Millennia of abusing these weapons have altered our planet's orbit." $\endgroup$ – user535733 Oct 12 at 16:53
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If we focus on Earth, gravity attracts any body, bullet included, toward the center of the planet, along a vertical line.

The anti-gravity will work the opposite way, pushing the bullet away from the center of Earth along the vertical.

As such it's not of much use: unless the target is right above your vertical, you have no way to hit it, while with a cannon, a gun, a bow, a javelin, even with a stone you can decide where you want to launch.

You can use a tilted plane to use anti-gravity to give some lateral velocity to the bullet, but once out of it, the bullet would go upward with an increasing velocity. Maybe useful for aerial targets, absolutely useless for target at your height or below.

If, as you state, the bullet is bound to normal gravity after leaving the gun, the impracticality lies in the fact that, to achieve gun like like velocity, you need long spans to accelerate.

For comparison, the exit velocity of the bullet of an AK-47 is 715 m/s. To reach it under the Earth acceleration you would need at least 73 seconds and an acceleration span of more than 26 km. Highly unpractical.

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  • $\begingroup$ Antigravity used as propellant, bullet is still bound to the same gravitational laws, right? $\endgroup$ – Adrian Colomitchi Oct 12 at 10:59
  • $\begingroup$ If you could, somehow, manage to focus the path of the bullet after the initial push, would it work then? Also, bullet is still bound to same gravitation laws. $\endgroup$ – Rosegold Oct 12 at 10:59
  • $\begingroup$ @Rosegold "focus the path of the bullet" is a phrase with no clear meaning. This question has already addresses how you can/cannot alter the path of the bullet using gravity/antigrav. $\endgroup$ – user535733 Oct 12 at 16:50
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  1. The antigrav field must be unidirectional, otherwise it's useless as a hand weapon in a planetary grav field - the field will jolt the gun upwards, far away from the huge mass down.
  2. if acting on a single direction, there's no difference from a firearm - the handler will fill the same recoil as when firing the bullet by gun powder - the impulse still conserves.

Even more, as a personal weapon, it can't propel the bullet way much faster than a chemical energy/hot gas one, otherwise the recoil will end by injuring the shooter (forget Eraser/EM-1, you can't fire a bullet at the speed of light). Assuming additional mecha tech, you'll still be bound by the impulse conservation (thus recoil) - just scale up to a nowadays heavy machine gun.

That is, unless you want to handwave the impulse conservation.

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  • $\begingroup$ The setting involves exo-skeletons, and recoil-absorbent shoulder pads. Don't be worried about the shooter. His enemies are using Gauss, and rail-guns on him. $\endgroup$ – Rosegold Oct 12 at 11:12
  • $\begingroup$ You just need to fire much smaller projectiles, solving the recoil issue. You will have problems firing at Mach 10 or faster, because the projectile will just burn up. $\endgroup$ – Starfish Prime Oct 12 at 11:25
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I think the only real advantage with the antigravity gun as described would be that you would not need propellant cartridges, although presumably you would need some power source so even that advantage might be limited. Traditional guns using high pressure gas derived from explosives can already project non-magnetic bullets at very high velocity.

The real issue boils down to the way the antigravity device works, what changes are needed to physics to make it work and what limitations then arise. If it can project an antigravity beam that is very focused it might have some further advantages, but if not I assume that the antigravity effects would work on the structure of the gun itself effectively applying a force around the gun barrel. Very high gravitational forces might also generate tidal forces in the barrel.

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How would a gun, that uses anti-gravity as propellant, work? Is it even practical?

The problem is that antigravity is ill-defined. Do you need some kind of negative-mass matter to generate it? Is it as weak as gravity? In that case, you'd need many, many earth-equivalent masses of negative matter to produce anything like a useful acceleration to fire a weapon, which would make it utterly impractical.

In a scifi context, when people say "antigravity", they really mean some kind of force like magnetism that works on any matter, with a fairly strong force being generated by a fairly small device. Calling it "antigravity" just seems to be a callback to classic scifi, or marketing, or just a lack of imagination. Given that such things are entirely handwavium, you can declare it to work however you like (but I wouldn't call it a "propellant", any more than electricty or magnetism is the "propellant" in a railgun or coilgun).

Since its non-magnetic, magnetic 'deflectors' can't bounce it off.

Firstly, railgun and coilgun projectiles don't need to be magnetic. In fact, they don't even need to be conductive... they can be pushed by a suitable and discarable "sabot" that separates from the projectile when it leaves the barrel of the weapon. Guns with chemical propellants could likewise fire any old material. Magnetic deflectors couldn't stop such projectiles, either.

Secondly, if you have a means of accelerating things via "antigravity", then what's to stop you making "antigravity deflectors" to bounce back any kind of projectile?

Thirdly, trying to use magnetism to deflect a bullet requires one hell of a magnetic field. Like, massively heavy field generators, big power supplies, big coolant reserves if you're using anything other than room-temperature superconductors. The field will also be brain and electronics scrambling, and will apply forces to any conductive or magnetic materials within its volume. Sure, you may have deflected a bullet, but you've just sucked a light-fitting out of the roof that's hit you in the head at bullet speeds, so you're not exactly winning.

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