My vote goes to the rifles described in Algis Budrys' 1957 novel "The Falling Torch". .276in bore, liquid-propellant bullpup weapons using ultra-compressed nitrogen in a bottle in the stock to fire the bullets much like a selective-fire air rifle (shades of Sherlock Holmes!) The second 3G3 sorcebook for BTRC's "Timelords" game system described a similar weapon that might be developed if caseless ammunition doesn't pan out (and at this writing, it seems that it isn't). Budrys' description of the weapon included such good ideas as a secondf check valve at the muzzle to reduce gas wastage, and a reinforced glassfibre/plastic gas bottle (they were replacable like the CO2 cartridge in an old Crosman pellet gun) that could take being fired from a mortar without bursting. Of course, then the DI shoved the same bottle under the roots of a hundred-year old oak tree, backed off, yanked a lanyard to open the valve- and the gas release was powerful enough to push the tree over. Not eaxctly "high-tech" by SF standards, but a simple, effective, and nasty infantry weapon..

easy. m41-a pulse rifle, from Aliens. hell the us military are trying to build and field it now!

Star Wars: Battle droids --> FCS Unmanned Ground Vehicles This is a stretch: Light sabers --> In the age of rifles, machine guns and what nots, the lowly tomahawk has become a favorite of the ground pounding community for that up close and personal kind of fighting. If you could make a light saber, they would carry them. Blasters --> High Energy Laser weapons. Ion cannons --> Particle beam weapons is next year's model.

The M41, AFAIK, was based on a real-life prototype from SciCon Systems in the UK; a 4.7mm bullpup over/under with a pump-action 30mm GL. (Yes, I know the ones in the movie were Thompson SMGs with Franchi SPAS-12 pump-action systems scabbed onto the underside.) So I'll agree it's very plausible. Not to mention a d***ed sight lighter than the H&K prototype the U.S. Army is still debating about. Another set of plausible weapons are practically everything in H.Beam Piper's stories. My favorites are the Akor-Neb handguns described in the Paratime story, "The Last Enemy". .20 cal. hypervelocity automatics (probably metallic-cartridge liquid-propellant, as he described them), with MVs in excess of 10,000 fps and roughly 1200 fpe (or 3,300 m/s and 1.65 KJ if you prefer MKS). The idea of a pistol the size and weight of a .22 target automatic with the hitting power of a 5.56mm assault rifle is definitely interesting..

hmm think someone slipped a digit in their calculating. a projectile moving at 10000 fps is going to pack much more punch than a 5.56 round is. depending on the mass of the slug probably 3 to 5x the KE of a 5.56 round.

It must have been me. The exact specs given by Piper are, "a .20 cal bullet at ten thousand foot-seconds", not specifying KE. Assuming a (roughly) 40-grain slug, I came up with 1240 fpe. I think maybe it should have been closer to 5000 fpe, or about the ME of a typical big-game rifle. The metallic cartridge was Piper's description, but I assumed liquid-propellant as the only way to get that much velocity out of what was basically a small-bore, high-capacity (20-shot magazine) pistol about the size of a typical modern 9mm. (I know, "assume" is a six-letter word that makes an a** of "u" and "me".) Stil, I believe the idea has some merit- ifd, that is, you could (A) really get that much velocity out of the system and (B) figure out a way not to be deafened by the muzzle signature, which would have to be pretty impressive, acoustically speaking :-)!.

wonder what the bullet is made of? 10000 fps means you are getting pretty close to melting the bullet from air friction which wouldn't be a good thing. more to the point that little sucker probably kicks like the proverbial mule.

another point is that a bullet like that would probably be pretty good at poking relatively little holes then exiting taking most of the KE with it. I think i would like a 200 grain slug at 2000 to 3000 fps. big hole and very possibly no exit at all.

According to Piper, the bullets fragmented on impact, sort of like the 5.56mm 55-grain, only a lot worse. This would "dump" all the KE into the target, rather like a Glaser Safety Slug, and Piper did state that a "peripheral" hit (i.e., limb or extremity) was either immediately or potentially fatal, much like taking a shrapnel hit from a grenade. IMHO, getting your hand or foot blown off by such a round is pretty definitely going to ruin your whole day. As to what the slugs were made of, Piper never said, but by the description of their effects, thay sound a good bit like the new "blended-metal" bullets we've been hearing of here recently. I think you probably could alloy such metals into a projectile that could tolerate being launched downrange at Mach 9+, and still give up all its KE on the first thing it hits. Of course, if you can do that, launching it from a small railgun might be easier on the shooter in terms of recoil; but you still have the problems of (1) the size of the weapon, rail system, and powerpack and (2) it's still going to sound like an F-15 mach pass every time you squeeze the trigger. As I said, I'm holding out for an integral suppressor on the little beast..

plus it'd lose its KE at a hellish rate. probably totally ineffective past 200m better off going with explosive rounds. no clever fusing- just a 1 second pyrotechnic delay.