^This. Regular maintenance is a must, and it’s not a stretch to imagine that some dingy guns you found in a looted gunstore in a post-nuclear wasteland might be a little worse for the wear. Then again, it’s not to the extent that most other games will represent it. Farcry 2 is hilarious, for example, with how it represent catastrophic failures.
Shooter skill matters somewhat with certain types of firearms. Glocks and some other compact semi-automatic handguns can and will jam up if you don’t hold your arm stiff and straight. The weapon requires recoil energy to cycle, if your arm is all spaghetti noodlin’ around some of that recoil goes up your arm instead of into the slide, causing stovepipes.