So, why bother with the light rifle?
It's sort of the lower range, from survival rifle to the poni gun; the poni gun is basically a modernized elephant gun with double barrels and five dice of damage, while the survival gun you're likely hunting wabbits.
However, from what I've heard from the Outremer, military snipers use the light rifle to take out guard dogs, and incapacitate protestors, probably why reporters wear helmets and bullet proof clothing. If the bullets are home made, harder to attribute liability.
Probably can take out mini drones, as well.
Modularization rule allows you to exchange the barrel, if specified, at no cost or extra weight.
Going by the above guide, the carbine, rifle and very long barrels allow you to keep the two damage dice, and extreme range of five hundred forty to seven hundred fifty metres, take out very shy wabbits.
Minimal barrel sounds like having none.
Short barrel for close quarters, if you have nothing else, fifteen metres being within twenty five, so you could use it without a stock.
Handgun and assault barrels might be more for marksmanship contests.
The survival rifle would, at least the really cheap ones, have a folding stock and a removable carbine barrel, which would be one better than the current models, since it would be basically in three pieces and even easier to stick into the backpack.
If you really wanted to militarize the handgun/light rifle, you bullpupize, and give it full automatic, which bumps up damage to two dice plus three.
In space, any hole in a spacesuit is potentially fatal, so armour piercing capability, advanced, which is plus two; down to earth against unarmoured opponents, wound enhancing with plus two per dice but lower penetration, which might work for the interior of spacecraft as well.
Explosive is only going to get you an extra dice, which might be something for short barrel.
I'm a little sceptical about special ammunition for light rifle, but if allowed, you have gas, sedatives, distraction, and possibly flechettes.