I have a new 2002 Rebel Vertical. I played w/ it once and it worked great. Next time I tried to shoot it, CO2 started leaking out around the barrel. After some dry-firing, the leak stopped. Then, I put my hopper on w/ pballs. I fired and it felt like the bolt was striking too hard, but the balls barely ROLLED out of the barrel. What's wrong?! I thought bout the cup seal but not sure...pleez help