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What's the difference between the two?

A railgun uses magnetic rails to propel a projectile along the barrel at exceedingly high speeds, correct? What is the operating mechanism of a gauss rifle?

Would using magnetic rails allow for firing speeds that are not possible with chemical weapons? What is a reasonable rpm estimate for an infantry-based railgun, and how quickly would the rails cause it to accelerate?

Mass drivers; are they merely huge railguns? If so, would the targeting system basically be 'point-and-shoot'? Would it be possible to cause the projectile to travel at fractions of c?

HemlockGrey wrote:What's the difference between the two? A railgun uses magnetic rails to propel a projectile along the barrel at exceedingly high speeds, correct?

No, the rails are not themselves magnetic. There is simply a lot of current passed through them (via the projectile), producing an enormous magnetic field.

HemlockGrey wrote:What is the operating mechanism of a gauss rifle?

If that's the same thing as the gauss gun, then it is the magnetic field produced by a series of solenoids. A precise timing mechanism for the activation and deactivation of those solenoids in tandem with the passing of the projectile is required.

HemlockGrey wrote:What is a reasonable rpm estimate for an infantry-based railgun, and how quickly would the rails cause it to accelerate?

You're not going to be able to generate the amount of power required for a decent railgun and still be able to easily transport it. It would be fine on a battleship, but definetely not for infantry. As for velocity estimates, that's pretty tricky. Although the underlying physics principles are quite simple, the movement of the projectile induces a magnetic field that inhibits the motion. This produces a truly ugly differential equation, one that I cannot solve (I've already tried this some time ago). Of course, ignoring the back-emf and friction, it becomes pretty simple (checks notes): v = 1.58533e-3 I sqrt(LW/m), where I is the current passed through the rails, L is length, W width (separation between rails), and m mass of the projectile (SI units all).

As for rate of fire, depends. Assuming you can get the rails cooled, then you're only limited by how much power you can generate or have stored.

HemlockGrey wrote:Mass drivers; are they merely huge railguns? If so, would the targeting system basically be 'point-and-shoot'?

I'm not sure about mass drivers, IIRC they're aimed at launching payloads into space, which probably makes them similar to gauss guns (a railgun would pulverize most payloads). Maybe not. A few minutes of Google'ing ought to dig up some information.

HemlockGrey wrote:Would it be possible to cause the projectile to travel at fractions of c?

For significant fractions of the speed of light (read: 0.001c or more)... only in space, with a very large railgun and a tremendous amount of current.