Thank you very much!
I would have gone with a tutorial to explain how everything works, but I didn't have time for that (started half a day late :P)
I am really glad people are figuring it out on their own though :)
Not necessary a tutorial, it can just be clearer feedback during gameplay.
If you match bullets, you have bullets flying to the magasin. You match guns and the new gun appear in the corner with a flash, particles etc. You can also put the bullet pattern next to the gun so that the player can associate both of them more easily.
And in a jam, if you don't have time to be fancy, just add text flashing briefly that explains the internal logic of the systems. "New gun acquired" "3 additional bullets" etc.