I got fed up with messing with airsporters and mercuries ages ago and had some steel piston heads made up, they take a single o ring and are half the size of the original nylon head so add a little more swept volume as well as the weight - gets the power up easily. you have to extend the cocking slot by a few mm as the piston rests a little further forward but they are an excellent mod, I prefer them to alloy heads.