I do not think it is the cap, as much as it is the gun. It seems that you can not the musket cap onto the nipple far enough. The first shot, which ends up being a mis-fire, only pushes that cap further onto the nipple which is needed in order for it to fire on the second shot. Than, it's a "mother F'er" to get the burnt cap off. Perhaps try taking a little bit off the nipple itselfs with some sand paper or a dremel. If the cap goes on all the way and snug, you should have a problem anymore. I didn't go that far, I just sold the gun to get something with out a bolt. Optima is what I bought. The bolt action guns foul up too fast, and the cap thing was the last straw for me.