Unlike most 12 gram powered guns, the Sheridans do NOT pierce the cartridge when you screw down the front cap. The piercing pin is actually on the cup seal, and pierces the 12 gram when the hammer drives it forward on the first shot. That's why the first shot is always low powered. I don't know why your second shot is also weak...that doesn't really make sense. But the first shot is ALWAYS weak. It's the nature of the beast.