I recently bought a used WC mk3 22 cal. Trying to shoot fx atomic 15.9grn. I can’t get the WC to shoot past 800fps. I’ve increased the reg from 80 to 150 and adj hammer accordingly. Also swapped from 500 to 600mm…no change. Also put a power plenum on and still no change. I switch the 600mm from pellet to slug and still no change. Any suggestions what it could be? Thanks