I'm not sure that this would be greeted with much enthusiasm. If I am unlikely to buy an expansion book filled with gear that works pretty much the same as the standard gear, but that has different explanations.
In any case, Traveller weaponry is generally the most reasonable extrapolation out there. Most sci-fi weaponry is utterly laughable because it tends to be distinctly inferior to current hardware in most important respects.
************Ummm...this is a sci-fi game. You seem to be missing the point. If we could explain how these new weapons worked to the point that we can with our current weapons we would have them on the market and be rich.
For instance, Star Wars blasters are inferior to modern assault rifles--they are no more accurate (and arguably less accurate) and have a low rate of fire compared with modern assault rifles. Star Trek phasers are even less useful in combat. A group of ACR equipped troops would wipe the Star Trek dustbuster-phase crowd out. (Of course, Picard & Co. would surrender before the fight could start, but that's a different story). Star Trek's dusbusters have no sighting mechanisms, which would make them pretty muich worthless in a real fight. They have a low rate of fire, though the ability to fire a wide beam may compensate somewhat. Still, I'd rather have an assault rifle, SMG or ACR.
***********I have never fired a blaster or phase pistol so, I can not comment on how lethal they are. However, I have fired a wide variety of modern weapons in my tour in the Marine Corps (M-16, M203, Mk 19, etc.) just to name a few. My time as a law enforcement officer taught me to shoot from the hip. Thus, not requiring any aiming devices. Also on that note, some of the best shots in this country don't aim at there targets. They allow there instincts and muscle memory to guide them. I remember the time that I actually saw a guy throw several half dollars in the air and with his revolver hit each one damn near the center (three coins/ four shots). If you could get me the manufactors spec for the Blaster and Phase pistol I would gladly do a comparison of the ROF for you. I don't know how many fire fights you have been in but aiming is not a factor.
Lightsabers are even less likely sci-fi weapons. I'll take out a dozen Jedis with lightsabers if I have an Atchisson Assault Shotgun.
**********Again, sci-fi game.
At the end of the day, the most effective way to kill someone is to hit them with a large dose of kinetic energy. And bullets are extraordinarily effective at imparting large doses of kinetic energy.
*************I think reading long posts about non-existent energy weapons might be a close second.
Regarding propellant, well, it's true that other propellants have been devised besides gunpower and its descendants, though the alternatives have been inferior.
**********Ummm...other planets, other life forms, other possiblities.
So as long as a planet has charcoal, sulfur and potassium nitrate, I think that gunpowder and its descendants will be the propellant of choice. Of course different explosive formulations might be found, but the end result is the same--an explosion propels a solid projectile at a target.
That will only change (IMHO) when we have incredibly light, cheap and rugged power sources that can power gauss weapons and lasers.
A planet that lacks gunpowder (or an alternative that is just as cheap and effective) will develop dramatically differently than Earth did. For one thing, I'd expect overall technological development to be significantly slower. The reason is that cheap guns did more to enable democracy and capitalism--the chief drivers of technological innovation IMHO--than anything else. A planet that lacks cheap, effective and easy to use weapons will tend to have economic and political power concentrated far more than the West (the center of technological advancement over the last thousand years or so). This is because alternative weaponry would be much harder to use effectively (i.e., swords and bows), and therefore require far more training. If such weapons can be countered by expensive armor, a small, professional warrior class can keep the aristocracy in power. That's harder to do when your knight can be shot off his horse by any peasant with a musket.