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.
"But we have our own dream and our own task. We are with Europe, but not of it. We are linked, but not comprised. We are interested and associated, but not absorbed."
Winston Churchill 1930