The TR-116 were made for the Dominion War, but if memory serves, they're a proto-type right? Were they put into the field?
I don't know that the show ever depicted that, but in my TNG novel A Time to Heal
, some Starfleet forces were equipped with modified TR-116s and later versions, which I dubbed TR-120s, though I flubbed the terminology of its exographic targeting sight (I think I called it exogenic, which makes no sense).
I kinda think they need a larger magazine or somesuch- it seemed like they were running out a lot in Destiny, but maybe that was just a full-auto thing.
Well, that's a major drawback of projectile weapons. Even with a caseless ammunition system (such as was developed by Heckler & Koch for its G11 advanced combat rifle in the 1980s), one has to balance the conflicting desires for more magazine capacity and lighter weight. Add too much capacity, and the weapon becomes too heavy to use effectively in the field; reduce the capacity to lower the weight, and your troops spend all their time reloading.
The TR-116s probably carry a 30– or 50–round clip of caseless ammunition (invented by Dynamit–Nobel, for Heckler & Koch). Basically, the chemical propellant surrounds the projectile and is consumed during the firing. There is no ejected shell casing, and the combusted propellant is used to drive the reload mechanism. Because it's a closed system, it has less recoil, making it more accurate.
I'd imagine that by the 24th century, Starfleet R&D has also added better stabilizers and developed lighter, stronger composite polymers for the weapon's shell.
All in all, the TR-116 and its cousin, the TR-120, are very sophisticated and very deadly small arms. Add in their monotanium projectiles with monofilament tips, and you have weapons whose accuracy, range, and penetration capacity surpass those of any standard-issue battle rifle currently in existence.