Has any one had problems with Airsporter/Mercury low power using none genuine alloy piston heads. I have had an Airsporter apart 4 time replaced the nylon type head that was sized with a alloy head , new Oring buffer washer and spring . .22cal and its only doing 8 ft lbs , fitted a Titan XS spring and use a genuine BSA O ring still the same. Also i have rebuilt a .22cal Mercury new alloy head , seals spring and barrel seal 9.5 ft lbs ?.