With respect to Ed's suggestion to "proof" at 10,000psi, be aware that Parker used about 10,000 psi as a service load ceiling for all types of 12ga barrels, so a "proof" of 10,000psi would be inconsequential. For 10,000 psi, just stick a Rem game load in that runs 1 1/4 at about 3 to 3 1/4 dre. TPS shows a proof load was about 13,500psi for early guns , then later at 15,000. TPS always contains answers to most Parker questions.
Drew, of course a person need not send the gun off to Maryland for testing , he can get all he needs right out here on the plains. Mitchell Cabelas carries these which they say a person needs for killing pheasant. Only 1 3/8oz at 1500fps, just what everybody needs, don't even have to lead the bird. Only $15 a box of 25, save your $420.