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And not some big space gun a mile wide, I'm talking more like "could you pack a nanogram of antihydrogen into a shotgun shell or rifle casing and fire a bullet with it?"

A few conditions and assumptions:

  • The gun is made from futuristic polymers, alloys, metamaterials or whatever that would allow the barrel to survive a fifteen megajoule explosion from the inside

  • The shooter is similarly cybernetically augmented to withstand the kick of the gun

  • The gun must remain effective and combat-ready (i.e. if the initial reaction destroys the bullet before it fires it fails)

  • The gun must be practical enough to warrant use. It doesn't matter if it's super expensive or needlessly flamboyant so long as it's still just as effective/more effective than normal firearms (otherwise what's the point?)

Could it be done? Could a sidearm that uses antimatter as a propellant work on the battlefield as a hypervelocity weapon? Or would it simply be too suicidal/too prohibitive compared to a normal gun that uses chemical or electromagnetic propellant?

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  • $\begingroup$ This is more of engineering issue similar to designing fusion power plant, in ur case either the bullet is vaporised or the escaping shock wave kills the user on the spot. $\endgroup$ – user6760 Nov 26 '16 at 7:42
  • $\begingroup$ Are you trying to make more powerful guns? Because propellant is not much of a problem, you can stuff way more power into cartrige even today - that would make both the cartrige and the gun significantly more expensive with just a tiny bit of performance boost, 10 guys with regular guns and ammo will take out one with cooler gun and ammo (and cost the same to equip). $\endgroup$ – Daerdemandt Nov 26 '16 at 9:44
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A regular gun uses an explosive that generates hot gas, and the expansion of this gas propels the bullet.

Antimatter annihilation produces a large amount of gamma radiation, (when protons annihilate they the direct quark-quark annihilation produces hard gamma rays, and an rain of unstable pions that soon decompose into more gamma rays and neutrinos) The gamma rays eventually deposit energy in the surroundings and you would get quite a lot of heating.

These gamma rays are quite penetrating, and will probably escape from the gun. You don't get a focused explosion with lots of hot gas to propel a bullet instead you get the gun and the the operator being irradiated. Even if you manage to shield the gun, there isn't the release of gas that occurs with regular propellants, so the bullet is not mechanically forced out of the gun at high speed. Its not a very good gun.

Producing antimatter in macroscopic amounts is 'hard' and managing it is also 'hard'. Gunpowder is great in that I can put some in a cartridge, and it just stays there. If I don't put a spark to it, it doesn't do anything. But antimatter needs containment. Containment is heavy. I'd rather not carry a 50kg particle accelerator just to keep the antimatter safe.

OK, suppose these problems are fixed, and the gun fires a bullet without killing its user. Is there any benefit? Muzzle velocities are not limited by the power of our explosives, but by the mechanical properties of bullets in air. If I managed to convert the nuclear energy of annihilation to the kinetic energy in a bullet, the bullet would ablate and slow as it passed through the atmosphere, I wouldn't get more range, or a more dead enemy.

An alternative to an antimatter gun is an antimatter tipped bullet. You would still have the difficulty of containment, but if this is handwaved away, a bullet with a nanogram of antimatter in its tip, designed to annihilate on impact would be a terrible weapon: a .22 sized tactical nuclear warhead.

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    $\begingroup$ Hot gases can be generated on spot, by vaporising material that immediately surrounds explosion. Generally, if the shielding is good but does not dissipate the heat, it would vaporise. As for speed limit, propellant does play a role here, but if you rely on hot gas to accelerate the bullet you're stuck around sound speed anyway. Other means - like electromagnetic acceleration - lack this particular drawback. $\endgroup$ – Daerdemandt Nov 26 '16 at 9:38
  • $\begingroup$ Sound speed? The initial speed of a standard bullet fired by a mass-produced FAMAS, for example, is 930m/s. You are hit by the bullet before hearing the explosion. $\endgroup$ – Ouistiti Nov 26 '16 at 12:06
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    $\begingroup$ By "Terrible weapon" do you mean: it's terrible, because the shooter also dies? $\endgroup$ – Borsunho Nov 26 '16 at 16:13
  • $\begingroup$ Where is this 50 kg particle accelerator? I would like to buy one... $\endgroup$ – kingledion Nov 27 '16 at 2:08
  • $\begingroup$ @kingledion Me too! I want one for Xmas. $\endgroup$ – a4android Nov 27 '16 at 5:11
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Taking the proposition that nanogram of antihydrogen converts into fifteen megajoules, this won't be a fifteen megajoule explosion it will be a fifteen megajoule pulse of gamma radiation. This sounds like too dangerous for the operator. Suicidal if the trooper knowing pulls the trigger or culpable homicide if the lethal hazard hasn't been definitively explained to the trooper by the relevant authorities.

Whatever technology is required to make a weapon use nanograms of antihydrogen as the propellent for a sidearm, it will have to be able to reflect or deflect gamma radiation in ways that absolutely minimize its harmful effects. It is doubtful if "futuristic polymers, alloys, metamaterials or whatever that would allow the barrel to survive a fifteen megajoule explosion from the inside" exist. To do that, requires segue into "magic" materials or technology. Gamma proof force-fields anyone?

Perhaps there might be "futuristic polymers, alloys, metamaterials or whatever that would allow the barrel to survive a fifteen megajoule explosion from the inside", but the structure and mechanics to make an antimatter propellent gun work will be most probably massive, multilayered and complex. Sidearms would definitely be out, an oversized howitzer perhaps. Remote controlled operation most assuredly. Sounds like the sort of weapon that ensures there are an arms limitation treaties.

The cybernetically augmented shooter might be more deadly and dangerous if he threw the gun and its antihydrogen ammunition at his target instead of firing it.

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No. You don't necessarily want detonation because too much of the force is lost in directions not along the barrel. And antimatter matter would detonate. Plus you'd get a lethal dose of gamma radiation, you're not shielding that without a whole lot of lead (my vest? yeah it weighs 400 pounds, but boy wait till the enemy walks into my line of fire...). Anyway, there's no known technology which would allow the stable storage of antimatter for more than seconds or minutes, so no you're not going to be carrying around bullets containing antimatter. Back to detonation, sorry for wandering. The most effective propellant for a weapon depends on lots of factors, but its burn is designed to be slow enough to accelerate a bullet through the barrel using the gasses released. Without some sort of magical force field technology, you're not doing that with antimatter+matter collisions.

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I actually use something like that, but with magic involved. The other answers are good but also missing one point. If you actually manage to fire the gun without having instant doom, i.e. the bullet leaves the barrel in the right direction, then there are still a lot of air molecules getting in the way of the bullet before it can reach its target. Imagine the bullet is somehow scientifically shielded against the air particles, how would the shield "know" that the target is reached? The shield can't be simply "used up" because then the bullet would only work on certain distances with the right wind. It could't act upon different "pressure" because I image the pressure is the highest when the bullet is fired inside the barrel. The only science-ish solution I see is "coating" the bullet in the barrel after being fired, e.g. midway out of the barrel.

This problem also applies to James' version of the bullet.

PS: My version of the bullet destroys soul on impact, resulting in death on contact. Very, very forbidden.

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There is a solution to this problem. Convert annihilation energy to electricity and power a tiny rail gun with it. A tiny handheld gun will give the impact of a 7.62 dragunov. The recoil would be tough to manage but it would be within the realm of possibility.

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I realize that you specifically ask about a gun that uses the "explosion" of annihilated antimatter to propel the bullet so this reply might not be what you want. But, doing it that way is not a good way to take advantage of the antimatter.

Antimatter battery and a electromagnetic mass-driver

Instead of using the annihilation of antimatter as an explosion (as it will not cause hot gasses, rather high energy radiation) it might be better to consider an advanced antimatter fuel-cell. Antimatter is held in some kind of containment and minuscule amounts are freed to annihilate. The tiny discharge of radiation is used by the fuel cell to charge electric capacitors.

The capacitors are then in turn used to charge electromagnetic coils which accelerate a magnetized bullet towards the target at high speed.

Benefits over a normal chemical gun is that only the bullets need to be stored (making ammo take less space - meaning one can have more of it). Also there is no discharge of hot/poisonous gasses which might be problematic in some environments. The antimatter fuel cell might never need a replacement due to it's energy density.

For a really endless gun - replace the mass-driver with a laser, or go half way and let the magnetic coils accelerate super-heated ionized gas.

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