A few mods to the factory valve turns it in to a much more powerful platform. Open the dropblock port to 1/4" ream and polish the valve throat to 5/16" turn a new peek poppet on a 1/8" drillrod stem and no valve return spring. Drill/tap the original valve stem hole and thread in a brass screw. Face it off and drill/ream for the 1/8" stem. Valve exhaust port drilled at 20° angle opened up to .300" breech and barrel also at .300". Modify the hammer to accept a factory Benjamin Bulldog spring and a new spring guide plus a 700mm barrel achieved 225fpe in .357 slinging a 145gr nosler slug at 836fps on the first shot but decline at about 20fps for each additional shot. Need to find the balance of power vs shot count but pretty sure at over 220fpe it's the most power that platform has produced. Could do even more if the dropblock was capable of porting above 1/4" and safe at a higher fill pressure. 
