Ok, jamming and freeing a jam (unjam <weapon>) are now fully coded. As was pointed out, if we were to turn it on, there would be a number of jammed weapons (12 to be percise) that would already be jammed. Several others are so dirty, they could jam the next time they're fired. Because of this, jamming is NOT
affecting anything right now.
You can 'unjam' a firearm while in combat. If its a simple jam, you might free it up. If its not a simple jam (or you're just unlucky), you'll need to take it apart.
To free up a jam you can't handle in the heat of combat, you'll need some time, a ballistics toolbelt and the knowledge and skill in caring for firearms. The idea here is that those of you with this knowledge can charge to unjam peoples guns (and modify them).