Q&A: Gauss Rifles

So, how would a gauss sniper rifle work in real life (i.e. What kind of kick would it have, would it make a sound, what would the energy consumption be, etc)

Well, you’ve hit on the problem with all energy weapons, there. Power consumption is obscenely high. The entire reason that modern rail guns are ship mounted is because they are extremely energy intensive.

I’ll stick a caveat here that I may be doing the math incorrectly in my head, but: a handheld gauss weapon may actually have a substantially higher energy requirement per shot than a ship mounted weapon.  The energy used is based on getting the projectile to speed. With rail guns this creates two factors. First, a handheld one will have a shorter barrel, meaning it needs to accelerate the object faster, and small arms have, nominally, higher muzzle velocities than artillery meaning, in theory, you’d need to get the round to higher speeds than you’d need with a ship mounted system.

I say, “in theory,” because the muzzle velocity of the prototype rail guns the US Navy is using are somewhere in the range of 2400m/s. Which is ludicrously high speed, and gives the weapon an effective range of around 100 miles. In practice that is a bit overkill for an infantry weapon, and you could scale that back somewhat. But, you’re still left needing to accelerate an object to several times the speed of sound in a tiny fraction of a second.

I’m going to make a guess and say that recoil would be slightly more severe than with a modern gunpowder firearm. The problem is still basic physics. You’re accelerating an object into motion, which means Newton’s Third Law will take vicious revenge on your shoulder one way or the other.

What I’m not clear on is exactly how much, because of two factors. First you’re probably talking about a smaller round, and second, it will probably be going much faster than a modern firearm. A 2mm tungsten needle would have less recoil than most conventional firearms today, but muzzle energy is calculated (in part) based on the velocity and mass of the bullet when it leaves the barrel. (This is an easy point of reference for how destructive a bullet will be on impact.) In order for that 2mm spike to be more destructive than a modern bullet, it would need to be traveling significantly faster. So any recoil you saved on the lighter round would be replaced by requiring a higher muzzle velocity to do the same work.

One minor perk is that, while the projectile would have a higher velocity after exiting the barrel, it would build up speed in the barrel, meaning the recoil would be spread out a bit further. Does this matter? Maybe, but on a handheld weapon, probably not. If the overall length of the barrel is 36″ and you’re talking about a velocity of a projectile leaving it somewhere north of 1500fps, the difference between that and ignited powder would be mostly academic.

While I’m not sure what the rifle itself would sound like, I’d guess some kind of electric humming, simply because the magnetic coils would pull a lot of energy, (the prototypes sound a bit like someone shorting out a transformer), the actual gunshot would sound a lot like a modern rifle at long ranges. Again, physics is here to apply unfortunate limitations.

The speed of sound is, roughly 343m/s (or about 1125 feet per second). Any physical object that exceeds that limit will create a small air shock as it passes. (Technically, the exact point an object will create a sonic boom varies based on elevation, humidity, temperature, barometric pressure, and probably a few other factors I’m forgetting.)

Most modern rifles send rounds down range at speeds of at least 600 m/s. Even most handguns will exceed the 343m/s threshold. At long ranges, the loud crack from a rifle is a result of the bullet breaking the sound barrier. Now, if you’re operating a gauss rifle, that’s still going to happen. You’re dealing with basic physics. Firing the rifle will produce a loud crack along the path of the bullet.

Probably worth remembering the term, “rifle,” is a bit of a misnomer here. There’s no actual rifling in the gun, and bullet stabilization would probably occur via fins on the projectile itself. Probably with some kind of sabot system.

The choice of tungsten above wasn’t (completely) at random. The atmospheric friction will create a substantial muzzle flash. Where normal firearms eject burning powder, a rail gun would be ejecting flaming steel or whatever the sabot was made of. Having a projectile that can withstand the heat generated by atmospheric friction, and ferromagnetic enough to respond to the coils seriously limits the options. As mentioned above, you can’t fire a steel slug at 2400m/s because it will melt. Tungsten on the other hand has one of the highest boiling points for a metal. (It might actually be the highest, I don’t remember off hand.)

While I’m not 100% certain, it’s entirely possible the projectile may produce a visible tracer effect from atmospheric friction alone.

Now, there is another caveat here. I’m assuming you use similar velocities to a the navy’s prototypes. That’s not strictly necessary, and projecting a cartridge at, say, 800m/s would have vastly different characteristics, and may not generate enough heat to melt steel. It would also require roughly 1/3 the power per shot. However, the power consumption would still be extremely significant.

Some other details worth considering.

Because the barrel is responsible for the speed of the shot, it may be possible to fine tune how fast the resulting bullet leaves the gun. Depending on the design, this could allow for a kind of multipurpose assault/marksman rifle that isn’t really possible with modern firearms.

As I mentioned earlier, the navy’s prototypes have an effective range of 100 miles. (Or 160 km). At those ranges it would be basically impossible to fire accurately without extensive computer control, and possibly some kind of satellite aided targeting system. However, there are a couple reasons to tune one that high.

First, drop and drift. Bullets are, as we’ve said before, physical objects. There’s an old physics experiment where, if you fire a gun (parallel to a flat surface) and drop an identical bullet simultaneously, both will hit the ground at the same time. Depending on the cartridge, this does become a factor sooner or later. Spitting a round out at Mach 7 will have very limited drop in the first mile or two, meaning it will be somewhat easier to predict where the round will land at those ranges. This isn’t fully necessary, but it helps.

The second thing is transonic speeds. As a bullet travels through the air, it loses speed. When it gets down close to 343m/s, it will drop through transonic speeds. When that happens, it will be overtaken and hit by its own sonic boom. This destabilizes the bullet’s flight, and effectively destroys accuracy beyond that distance. The initial speed determines when that happens, and by extension, how far you can fire the weapon. If you can radically increase the initial speed of a bullet, you extend the effective range. This is part of why that prototype is so impressive.

Incidentally, if you get the velocity over, about 11.7k/s (so a little over four and a half times what the prototypes fire), you can put a round into orbit. Not particularly relevant for the question, but worth knowing. (Also that’s Earth’s escape velocity. It wouldn’t be the same for other planets. For example: those same railguns can achieve lunar escape velocity now.)

Of course, the biggest issue with these is still power consumption. Regardless of the factors, you’re still using electromagnets to propel a slug of metal to hypersonic speeds. With modern energy technology, that’s not really feasible.

-Starke

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