Herter's offers a 1 oz. Field & Target @ 1290 fps, a Select Field Dove & Quail 1 oz. at 1250 fps, and the Target LR 1 oz. @ 1060 fps.
B&P Competition One 1 oz. at 1160 fps is 6530 psi.
I suspect the 9000 psi is the Field & Target.

If the chambers have been lengthened, the wall thickness at the end of the chamber and forcing cone is critical.