>>115136784So I used to think this was stupid, but I have a hypothesis on why his Steve's gun jammed. It's mostly based on theoretical physics and time travel.
The gun jams to prevent a chronological paradox, as if the gun fired, it would likely leave a empty bullet or cartridge behind. This could potentially leave a bullet in the past before guns were invented, which wouldn't make sense for the passage of linear time, as it would imply something existed before it's creation. Reality wouldn't make sense of it, and that would cause zero sum of existance.
Steve and Diana aren't included in this paradox were supposed to travel back in time, and since no bullets are found in any archaeological digs, Steve wasn't supposed to fire his gun because reality is ensuring the causality of a chronological paradox by jamming it.
Its a dumb theory, and I'm probably wording it poorly, but hopefully it makes a little sense to somebody.
>TL;DR - To prevent a potential chronological paradox, reality prevents Steve gun from firing, as the discharge might leave behind evidence of guns existing before their time, which would basically zero sum all of existance. 
