High-Tech Weaponry
A build it yourself Gauss gun!
No, really, you can actually make this sucker in your own basement. This website, in Russian and English, shows you how. It takes you through the process, step-by-step, in somewhat broken English. And, it makes a pistol, not a rifle, which is doubly cool. So, this isn’t a “firearm”, per se, is it covered by the same rules? I’d imagine so. It would be, basically, a concealed weapon. It looks pretty effective, too, based on the photos(here and here). And, because it doesn’t use an explosive charge, there’s virtually no sound when it discharges. I see all kinds of applications for this little sucker.
Look out Traveller, here we come!