I am pretty sure it is 15 pumps. At some point you will not get a full dump. That point is heavily influenced by pellet weight, the heavier pellet the lower the point at which a full dump will not happen.
I would not pump past 12. IMO, owning a Steroid and a standard 392, anything beyond 12 pumps for the Steroid is abusive and anything beyond 8 for the stock rifle is abusive. That is an opinion of course.
I leave 4 pumps in my stock rifle and 5 or 6 in my Steroid. I just rebuilt my stock rifle due to the valve being severely corroded. It has the Twin Spring Mod, some port clean up matching and plenty of silicone grease to fill the space between the valve body o-rings. The TSM makes pumping noticeably easier on later rifles that have a single valve body spring. The "stock" 392 rifle does 650 fps on 8 pumps with the CPHP and the Steroid does 715 fps on 8 pumps.
