You can come up with all that based on a cutscene? You have got to explain how you do that.
The weapons used in Hallfight have several salient characteristics.
Extremely large apparent calibur.
Abnormal lack of noise for a gunpowder weapon.
No apparent shell casings.
No apparent ammunition supply.
This leads to several conclusions. They are not (with one possible exception, apparently a squad-support grenade launcher) chemical-propellent weapons as we know them, else they should be significantly louder in a confined space like that. The are not lasers or other directed energy weapons, because such weapons would not
strike sparks from something they were unable to penetrate. Since they must be firing physical rounds, the rounds they are firing cannot possibly be the same size as their muzzles because then they should have fired about once each and they clearly fire much more than that.
This leaves us with a weapon that must be firing physical rounds significantly smaller than the size of its barrel, which are
not discarding-sabot ammunition. Force-field based craziness is out of the question since it was only a little while ago that anyone developed relatively undirected fighter shields. Gravitics are, I suppose, possible, but we've never seen the GTA/PVN/GTVA use any gravitic-based weapons so I doubt they have the technology or the fine control. Magentic suspension and acceleration is pretty much the only option for doing such a thing.
The lack of physical contact with a barrel and the sheer complexity of attempting to spin a round for stability via magentics means that some kind of rifling effect is probably out the window, but on the other hand extensive computer aiming support is almost certainly a given so it's possible the weapon would be quite accurate...if not for the fact you have a crapload of magnets in the thing and it's being used shipboard amidst all kinds of magnetic fields and electrical currents. Given all these, it's probably no more accurate than a modern assault rifle and with the amount of computer support you could build into a similar projectile weapon, not very accurate at all by the standards of the time.
The interchangeable and versatile nature of ammunition is easily divined. There are two main bottlenecks in such a thing: size and and rifling. This is why shotguns have a much greater number of ammunition types then rifles. The GTVA's materials engineering and miniaturization has doubtless advanced so that they can produce rifle-caliburish rounds of many different types, and the weapon I propose would be ideal since, lacking physical contact with any part of the barrel, you could get away with a variety of different shapes.
