I believe we have been able to compensate for that now. Also with a powerful enough laser you could ionize the air which should help prevent this.
[MOO2]Personally, I drop Mass Drivers for Graviton Beams as soon as I can.[/MOO2]
I always thought the point of Magnetic Accelerator was the near-light velocity made aiming easier and / or made combat at extreme distances possible.
For the Navy it is.
Something that you could carry around to go hunting with no.
The hand guns in the books use little beads for hand held guns, so think of the recoil of sending a bb out the barrel. You’ld have more recoil than a typical bb gun, but less than a 9mm pistol.
They can send an electric charge through the ionized air too. It’s a design for some tasers already. You might as well try to fry somebody two ways at once.
From a physics perspective, I’d think recoil issues would be less for a rail gun: first, you’re not accelerating all the propellant gases, and second, the acceleration would be slightly more gradual, so a smaller peak force.
FWIW, conventional firearms have a muzzle velocity which is limited by the speed of sound in the combusting gases (which is usually much higher than the speed of sound in air at STP). Railguns have no such restriction, but the engineering of a reusable hyper-velocity railgun is hard.
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KE penetrators have been used as anti-tank weapons (by tanks), for decades. They have a muzzle velocity around Mach 4-5.
I think the point still stands, the advantage of railguns is that it can be made to go really really fast. For a hand-held weapon, it means you can use a much smaller projectile (bullet) and still do the same amount of damage to the target.
Not true, actually. The destructive capability of a projectile depends mostly on its energy, while the recoil depends on momentum. Kinetic energy scales with the square of the velocity, but momentum is directly proportional to the velocity. So if you have a given amount of destruction you want to do (i.e., a given energy), and you make a gun that can get the projectile twice as fast as the old kind of gun, then the projectile will only need to be 1/4 the mass. 1/4 the mass times twice the velocity would mean that the new gun would only have half the momentum (recoil) of the old gun.
Anybody who remembers the classic Battletech game after they introduced the rules for the ancient Star League technology and later the return of the Clans (who had spent the intervening time away from the civil war perfecting the old technology) should remember the Gauss Rifle, which was essential a magnetic accelerator. In fact, similar weapons were featured in FASA’s other big game, Renegade Legion, where they were referred to as Mass Driver Cannons (MDC’s for short).
Besides giving it tremendous range and potential for destruction, Battletech twisted the normal ballistic rules with the Gauss Rifle. First, as H3Knuckles mentioned in the OP, the ammunition has no propellant or explosive, consisting of solid nickel-ferrous slugs. Even a direct hit on the ammunition store would not cause it to detonate. On the other hand, a critical hit on an unprotected part of the weapon itself would cause the capacitor to loose its fury on the carrying vehicle, resulting in a spectacular and probably crippling explosion. Finally, since the vehicles carrying such weapons were powered by fairly compact fusion reactors, there would not be any problems with supplying the kind of power you would need until you ran out of either targets or ammunition.
If they could get around the wear-and-tear on the barrel, I could certainly see something like this mounted on a ship with a 21st-century fission reactor, or even a shore installation…
… but minus the 30-foot tall walking war machines, I’d kinda have to wonder what you’d be shooting at.
Re: the recoil: for a true railgun (rather than, say, a coilgun), some of the recoil force is directed outwards – perpendicular to the line of motion of the projectile. Also, they are essentially arc-welding themselves with every shot (not quite, but close enough). Friction in a true railgun is much higher than in a coilgun, and (I would surmise) much higher than in a conventional explosive-powered projectile gun, as well.
Anyway, they won’t have as much back-directed recoil as a comparable weapon, but there will still be recoil; the amount of which depends on the mass of the projectile and the speed to which it is accelerated. The formula’s been hinted at above. 
Aside: What most people think of when the term railgun is used is actually a coilgun. In a coilgun, there is no electrical connection between the accelerating coils and the projectile; in a railgun, it won’t move withOUT an electrical connection between the parallel rails and the projectile.
The advantage of coilguns over railguns is that they do not suffer from the brutal wear and tear on the ‘barrel’; the downside is, they cannot propel objects nearly as fast.
Lotsa good stuff on the 'net about these things, but for starters check out Wikipedia: Railgun. A Google search will pull up lots more detailed examples, as well.
How could this possibly reduce backwards recoil momentum at all, other than transferring it to the air as in recoilless rifles?
I’m not sure I understand your question, honestly. Or perhaps I misunderstand the word perpendicular…
What I mean is, the propulsive force of a railgun is caused by an electrical current passing from one rail, through the projectile, and through the second rail. This sets up a strong magnetic flux, which ‘pushes’ the projectile down the rails and hopefully into the target. The projectile ‘pushes’ back based on the usual laws of physics.
Part of this force is not directed backwards, however; it is directed outwards, pushing against the inside edge of the rails. If they are not sufficiently braced, they’ll tend to fly apart long before useful velocity is achieved, breaking the circuit and causing the projectile to simply sit there.
In a gas (explosive) powered weapon, recoilless rifles excepted, the pressure in the chamber has one direction to go - out the barrel, pushing the projectile in front, and pushing equally hard in the opposite direction. Since the railgun uses a traveling magnetic field rather than a pressure chamber, the force is ‘pushing’ outward rather than directly backward.
Think of it this way: the recoil force is still there, but the vector is changed.
Does that make sense now?
Yeah, I know a little physics, thanks. That’s why I wrote:
Ya’ know, science fiction, and all that, in which physically impossible technologies, like FTL drives, impenetrable “force fields”, and zero inertia space drives are commonplace?
You know, like fiction?
Railguns can operate in a vacuum. (That’s somebody’s cue to explain how a gun could be engineered with a built-in occident or whatever. Go to it! 
)
Also, quote from Jim: “Rail Gun: goes back at least to around 1970 and the late Dr. Gerard K. O’Neil’s “High Frontier” proposal. He proposed using it to shoot metal ore off the Moon into Earth orbit for use in building BIG orbital space colonies (the size of mythical Babylon 5 of Sci-Fi fame, or even larger), so the idea undoubtedly goes back even further than that.” http://blog.wired.com/gadgets/2007/01/us_navy_invents.html
The reason recoil will be significantly less according to a link I found, is because the propellant isnt being ejected from the barrel as well.
So the only recoil created is from the round, rather than the plume of propellant adding on to it, because the propellants ejected mass is also part of the recoil equation.
So you wont eliminate recoil, but will get a benefit by eliminating propellant as part of the overall mass being accelerated. Eg if you have 1kg of mass and 5kg of propellant, you’ve managed to reduce the total mass being accelerated by 5kg.
Otara
Why wouldn’t a gunpowder gun work in a vacuum (besides purely mechanical issues like loss of lubricant or vacuum welding)? Despite what Firefly says, real propellant doesn’t need external oxygen to ignite.
Sofaspud – Perhaps I’m misunderstanding you. It doesn’t matter what kind of sideways forces there are in a given projectile thrower – zero, more, less, or a force spinning the barrel. The force on the projectile has to equal the recoil force directly backwards on the thrower. So the fact that a railgun exerts a sideways force on the rail has no relation to how much recoil backwards it has.
Plus, of course, a gunpowder gun has pretty significant sideways forces. The expanding propellant gases push on all sides: the projectile, the rear of the barrel, and the sides of the barrel. It’s just that if the barrel’s strong enough, the forces on the sides of the barrel cancel each other out. And if the barrel’s not strong enough, well, then you don’t want to be there, of course.
IMO, that’s the biggest drawback for a laser weapon - line of sight.
You would normally want a cannon situated in a defendable and difficult to reach location. The ability to use rockets or gravity to change trajectory helps to bend the payload around your protective barrier (buildings, mountains, curvature of the earth)
I have no cite, but I can’t see a reason why it wouldn’t. Gunpowder, IIRC, contains its own oxygen source, right?
I’ve been reviewing my sources on railgun tech, and it turns out I was mistaken. Otara nailed it:
What I appear to have been doing is misremembering how the Lorentz force worked, and conflating that with the way the magnetic flux traveling along the rails worked, and coming up with the (incorrect) premise that the recoil vector would be altered.
So, to clarify: recoil is felt in line with the rails, directly backwards, opposite the vector of the projectile being accelerated.
The Lorentz force isn’t applicable for recoil calculations, so we’ll ignore it.
And the sideways force that I thought was the redirected recoil force, is actually the force generated by the magnetic flux itself. It’s very powerful and requires that the rails be braced against it, and it does exert itself perpendicularly to the vector of the projectile, but it’s not caused by the projectile and is not part of the recoil. Essentially, it’s like holding the same pole of two magnets near each other; that’s the force that’s trying to spread the rails.
(And, while partially inaccurate, this gives me the highly amusing mental image of the railgun projectile being squeezed out like a zit between two magnetic ‘fingers’. Heh.)
Strikes me that rail/coil guns are a technology that’s proving to be a real bastard to translate into anything practical
The idea’s been around since at least 1845 but (a bit like fusion power) actual breakthroughs seem a perpetually just around the corner
My WAG is that ram accelerators will be made into practical weapons and/or micro-sat launchers long before electric propulsion gets anywhere.
Although lacking the SF “Gee-Whizz” of rail/coil guns, conventional guns (even without using a light gas intermediary) seem capable of being used as launch platforms, with political and financial problems being harder to overcome than the technological
(though the speed of sound in the propellant gas sets an upper limit on speed, as others have pointed out)
As to recoil, I guess that’s the reason the reason the apparatus in Snarky_Kong’s vid is mounted on wheels.
Although it’s true that in normal gun the propellant gas adds to the recoil, a muzzle brake can offset that.