Thanks for the link, Dave. I only glanced at some of the posts, but I shall read it through later.
Anyway, I don't think there's any particular advantage to using a rail gun in
space, except as a type of "engine." Although there
might be advantages in general. And you are correct that gun powder performance can be affected by cold—even within the temperature ranges found on Earth.
Can a "rail gun" be miniaturized? Any futurist or sci-fi writer will tell you, don't bet against the future. The more firmly one denies the possibility of something, the more likely it will turn up as a reality tomorrow. I think the "pulse rifles" in
Aliens were supposed to be EMP weapons, as I don't recall seeing any casings flying around. (It's been a while since I saw the movie, but there is one point when the lieutenant describes the ordnance as "caseless." Of course, the weapons could still be caseless while using a propellant-and-projectile stack like
Metal Storm technology.)
Deckard's pistol from
Blade Runner may also have been EMP, as I remember power lights on the side. And if one can get a good look at the prop, it does not appear to have an ejection port.
So, what might the advantages of an EMP weapon be? For one, the operational temperature range mentioned above. Electronics—particularly batteries—can be affected by cold, too, but there are plenty of space probes deep in the black that seem to be doing just fine. Of course, they may have a constant "body heat" keeping them going just from the power supply. In that case (or caseless as it may be), an EMP weapon may have a broader operational temp range
as long as the power supply holds up.
I think an EMP weapon may have potentially higher muzzle velocities, but there are a number of factors that can affect that. A longer barrel will produce greater velocities, as the projectile will be in the "motor" longer. (This also holds true for today's firearms—more time for the expanding gas to push the projectile.) However, you don't get something for nothing—the person holding the gun will have to tolerate greater and greater recoil for those higher speeds.
But high muzzle velocity is not always a good thing. The Arnold Schwarzenegger film
Eraser features a rifle-sized rail gun. The characters talk about it having a tremendously high muzzle velocity, but then we see every target picked up and thrown a great distance—which is exactly what would
not happen. The higher the muzzle velocity, the greater ease with which the projectile will penetrate the target. But that's good, right? It all depends on what you are firing at—armor plating, or a soft, squishy enemy.
"Stopping power" is a non-technical term that has been debated for almost as long as Mankind has had guns. A .45 caliber slug is a very big, very heavy bullet, and typically produces slower muzzle velocities than smaller diameter rounds. However, that big, heavy bullet will generally
knock down the target.
The 9mm "Parabellum" is probably the most popular round in the world. (For comparison, the .45 ACP is 11.43mm in diameter.) The 9mm is smaller, lighter, and typically produces muzzle velocities significantly higher than a .45. However, the 9mm also has the nasty tendency to penetrate (pass through) everything. Remember the scene in
The Last Crusade, the third Indiana Jones movie,
where Indy fires a Walther P38 at three Nazi soldiers fighting him on top of an old tank? That's no joke. So higher muzzle velocity is not always better—although there are ways to control it.
A 9mm FMJ (full metal jacket) will penetrate targets most easily. FMJ means the bullet is covered by copper (typically), rather than being a naked lead slug. A "hollow point" bullet is one with a dimple in the nose and cuts in the jacket around the nose so that the projectile spreads open like popcorn when it strikes a target, thus flattening and expanding the cross section. This causes the bullet to slow down more efficiently and deliver more energy to the intended target (known as
hydrostatic shock), rather than passing through, which wastes energy. This sounds nasty, and is (shooting someone is not a game), but hollow points are also called "safety" rounds because they decrease the likelihood of the bullet penetrating the target and hitting unintended targets beyond.
Even more efficient than hollow points are "frangible" bullets, which completely shatter when they hit a target. That makes frangibles sound completely useless, right? I have a video documenting a range of pistol ammunition from .22 LR up through .45 ACP. Each caliber was also tested with FMJ, hollow point and frangible. The "man-like" target was a panel of pine wood in front of a gallon water jug. Except for the very smallest calibers, all the FMJs passed completely through. Some hollow points passed through, although tended to make the water jug "explode" where the FMJs did not. The frangibles generally did not pass through at all and made the water jug explode while flipping it through the air. The big test for me was the same spectrum of ammo on a car door. Believe it or not, the .45 entered the door, but did not come out the other side—this is sheet metal and plastic. Long story short—in my estimation, the 9mm frangible was the "best" performer. While it penetrated both sides of the door, what came out the other side was a tiny fragment too lightweight to hurt anyone, let alone kill them. (The .357 and .44 magnum were overkill, in my estimation, at least so far as self-defense is concerned. Longer barrels, more recoil, more noise, more overt destruction.)
So, a high muzzle velocity alone is not necessarily good, but it can be controlled to the best advantage. The military uses many rounds even smaller in diameter than 9mm, such as the 7.62 and 5.56. Both are pointed and have a bigger charge behind them than a civilian would use in a self-defense pistol, but then they may also have to penetrate body armor. Both are also "longer" in aspect, which makes the bullet "tumble" after breaking the surface of a target. (Not the same thing as a hollow point or a frangible, but better than making a clean penetration.)
To round up: Operational temperature range may be one advantage to a hand-held EMP sidearm. Muzzle velocity alone is no advantage, but that can be controlled with the type of bullet to help deliver more energy to target—an EMP weapon might also be able to vary muzzle velocity electronically. The one other advantage might be the ability to carry more rounds because there is no casing and its associated charge (which can add up to a lot of weight).
