How Would an Anti-Gravity Gun Function

Question

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.

Answer 1

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.

Answer 2

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.

Answer 3

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.

Answer 4

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.

Answer 5

The term "anti gravity" is rather vague.

At its most literal it simply means the ability to annul the effects of gravity within some domain, which wouldn't really be useful for a projectile weapon (*1), but more broadly it means the ability to offset the acceleration due to gravity with another accelerating force in a direction of your choosing; if the two happen to add up to zero then that's nice for softly floating around, but why stop there?

The primary defining characteristic of a "gravitational field" is that it applies a force (to anything within the field) in direct proportion to its mass. Your ability to control the shape of this field determines what you can do with it. The trick is to do this without moving a planet-sized mass around.

1. We can already do "artificial gravity" simply by using a rotating inertial reference frame. In this case, the field is the centripetal "force" that increases with the radius, which means the outside tends to get squished. However this has already been adapted to make a space trebuchet.
2. If you have some fantastical local field generator that works in a non-rotating inertial reference frame, and you can direct and focus it in a way that makes the field uniform over the whole of the projectile, then you essentially have dial-a-yield: beyond the limits of your power source, there's no limit to the "muzzle velocity", as even the air in front gets pushed out of the way by the field.
3. If you have a not-quite-so-fantastical local field generator, then the field gradient will be your limiting factor, as you don't want to rip the projectile apart, or compress it so much that it immediately explodes once release from the field.

(*1: gravity annulment wouldn't make for a useful projectile weapon, but you could make a weapon that simply picks up your opponents, and drops them from a non-survivable height.)