You have to remember that this is not a War sim, this is a post-apocalyptic game. Guns breaking down is in combat, I believe, 100% intentional on the part of the designers.
And it has to be. I've said previously, many many pages ago, that I feel the mishap rules need tweaking, & I eagerly await the beta rules to see what's been done here.
But mishaps absolutely need to be a thing because, lest we forget, we are going to see people using improvised weapons.
Yes, I know players don't like them, because they want a world where you can somehow find yourself carrying an obscure prototype of which only seven were built, because you got it off an arms dealer in Krakow, etc., but the fact is that private gun ownership in Poland is low & even if the war has killed 75% of the population, there are still more people in Poland than there ever were soldiers, of all sides, which means that bangsticks are not as abundant and widely available as you might think even if you choose to forget that many of the original complement of military bangsticks imported by various combatants are now buried, ruined, nuked, or lost. So the upshot is, zip guns and the like are part of the game. (And I like that there are so many improvised weapons in the rules, personally.)
And improvised weapons will tend to fail, sometimes in catastrophic ways.