I've logged over 200 hours happilly, with big guns, small guns, and energy weapons. Guns don't jam in the sense that you need to unjam them. But when your weapons do degrade to a certain point, say, 25% or less in the Condition bar, your gun will jam in the sense that reload will take almost twice as long to do. So.. yes? and yet, no. You're most likely going to find plenty of weapons to use to keep your gun in good shape, or, enough caps (in game $$$) to keep getting them repaired by certain NPC (Non-Player Character). You'll most likely keep a variety of weaponry in your inventory, or even hotkeyed, that you can switch too if need be. Hope this answered your question, and helped others too!