I've used and taken care of an Rk 62 assault rifle for a long period of time during my conscription, and after each and every time the rifle was taken from the cabinet and taken somewhere, not necessarily even used for other than carrying it around, it had to be cleaned and oiled before it was put back.
Every time you fire a gun, parts move and filth gets everywhere. If you do not remove whatever it is that's gotten to a place it shouldn't, it will wear out the parts, until when it's done that enough the parts break, as their structural stability is not what they're supposed to.
So, being a curious guy that I am, I decided to do a small scale test to see what'll happen to a small spot I didn't oil. In just a couple of days that small spot was rusty, badly so. Do note, the gun rusted while it was in the cabinet, not when I carried it around, so the damage was actually less than what it could have been. It took me a little while to get the rust off and in the end, the spot and the rust were so minimal nothing happened, and the gun passed all checks done by professionals when I returned the gun back to the armory for good.
Also, running in the woods caused tiny pieces of twigs and such to somehow manage to get into the gun.
My point is this:
If I didn't take care of my rifle at all, it would have become useless in a week or less, even without firing it.
I'd say if they gave me a couple of hundred rounds to fire, in one day of running in the woods and shooting all those bullets, the gun would jam or have parts break.
Underrail guy doesn't clean his guns... ever. Using firearms, he's constantly allowing dirt to go to the wrong places and cause the parts to wear out more than they should.
Laser weapons are probably more fragile by default and certain parts will wear out even if he cleaned the gun, and he'd have to replace parts anyway.
You will also have to understand that sometimes you have to ignore realism in favor of game balance.