I took one look at this, and immediately thought "You know, I think I saw this one in SR4 Arsenal."

the author doesn't seem to be very well-informed.

i'm pretty sure the greatest promise of railguns is that you don't need to accelerate the propellant and that you accelerate the projectile over a distance rather than all within the first little bit of barrel.

meaning that you can afford to cram more kinetic energy into the projectile (either by making the projectile faster or heavier) without unduly increasing recoil. as in, the promise of railguns is not that they are (or can be) less lethal (because seriously, making projectiles slower is not something we struggle with as far as i'm aware, and i can't imagine a railgun beanbag launcher working very well), but rather that they can be *more* lethal.

(also, i'm a bit doubtful the double helix rails could impart enough spin to make a substantial difference).

I'll take your word for it. I'm a programmer by trade, not a mechanical engineer.

The principal limitation of everything which propels projectiles with expanding gases is that the speed of the projectile is limited by the speed of sound inside the propellant gas. That is why light-gas guns (essentially airguns but using helium or hydrogen) are used for hypervelocity reasearch, the speed of sound in light gases is far higher than in air.

Railguns don't use expanding gases, therefore they circumvent this limitation altogether.




His argument is that you can "dial down" the current on a railgun more easily than it is to reduce the propellant of conventional munition on the fly -- which sounds somewhat obvious. But I'm not convinced that merely reducing the muzzle energy of a conventional projectile makes good less-than-lethal option...

That looks like a Warhammer 40K Tau pulse rifle.

[img]http://media.moddb.com/images/mods/1/6/5152/57623.jpg[/img]

how do they manage to launch projectiles further using bigger guns if that is the principal limitation? it seems like a bigger gun should have essentially the same range limitation if it has the same speed of projectile...

or is it just that a bigger gun can launch a shell big enough that the blast radius can replace accuracy? or perhaps just less influenced by wind, so it would actually be more accurate.

in any event, the promise of railguns is higher energy, not lower energy =S i got that part right i guess.

(and i am also inclined to agree that being smacked in the face with a thrown metal slug doesn't sound like a particularly good less-lethal solution, even if it isn't super fast).

I'm not an expert in guns here, but as far as I can tell:



I don't understand this : in a rail gun, the projectile is accelerated by passing an electric current through it between two rails… Seeing how changing the barrel length on a rifle change the energy and power (and reading several times how carbine version of rifles lose a lot of stopping power, even here), I'm pretty convinced the projectile is accelerated all along the barrel length. As has been said, the current limitation for classic gun is the propellant speed of sound.

There's an argument concerning recoil. Well, I'm not convinced, to say the least, that one can expect to really lower it. If you want to give momentum P to a particle leaving your rifle, your rifle will have momentum P toward you. Is the recoil on a rifle mainly due to the bullet, or to the gas?



A heavier projectile with the same initial speed will go further than the lighter one, because its mass (and so inertia) is growing with the cube, while its surface (which cause air to slow it) is growing with the square.

recoil is mostly from the bullet, but obviously some of it is also from the gas. precisely ratios of bullet to propellant depends on a lot of factors, but i think it would be fair to say that in most cases, the great majority of the mass comes from the bullet, not the powder. still, some does come from the powder, and that should be reflected in reducing recoil required to launch a projectile of a given mass (meaning you can put a bit more energy into the projectile and still get the same recoil).

still not understanding why the speed of sound in the gas caps the speed of the bullet, but i suppose that's a bit beyond the point of this site.

main point still stands: nobody is researching railguns as a less-lethal option that i'm aware of. rather, the primary focus is on making them *more* lethal.

Thanks for the input on recoil. So I guess it's still true that recoil will not be a major improvement from rail guns. I'm pretty sure they will come with their additional problems too, due to heating, cumbersomeness, etc.

I don't know if one mentioned it, but the reason we talk about speed of sound is that a gas cannot dilate, on its own, faster than the speed of sound. So if the gas don't move faster than the speed of sound, it cannot push the bullet faster*.

Your main point still stands. I agree.

Less-lethal stuff is limited by it's ability to splash energy on a huge area. Probably if you make the calculation on a standard bullet, you'll find that for it to give the same energy as a punch, its geometry will lead to your skull breaking…

And of course Less-lethal problematics are also more linked to the human body not being easily neutralized without risking to kill it. Soporific gas are banned in France because they can kill, some people are mutilated with flash balls, and some people had infarctus after being taser shot (and some didn't feel it).

Or a bit more graphic, the shock wave from the explosion is the same as a sound wave and therefore does not move faster than the speed of sound inside the propellant gas (it can still be plenty faster than the sound in the surrounding air).

However, this is just an upper limit, how much energy the bullet ends up with depends on more than just the velocity of the shock wave. Hitting a car with a supersonic bullet won't move it much (because the energy transferred it too small), whereas three people pushing relatively slowly can easily get a car to move


There might be other applications for "dial-a-speed" weapons, though. Dial down the speed to avoid overpenetration, dial it up to make a shot count or when the weapon is braced to deal with the recoil...a smartlink could even do it automatically base on distance, wind, posture, tightness of underwear...

Nevertheless, speed of sound will change mainly with temperature (raise with square root) and molar mass (diminishes with square root). So I'm wondering at what temperature the powder is burning, but going at more than 5 times the speed of sound in cold air (1500 m/s)(such as APDS) already implies to reach 7500° in this case. So either I'm missing something (and that's really possible), either it's pretty hard to really go past 2000 m/s…

I'm really skeptical about the dial-a-speed applications. Bullets are designed to have their optimal efficiency at a speed they are designed to be fired…

No you are perfectly right, which is why light-gas guns are a thing.