A typical Pigeon load of that era would have been 1 1/4 oz. 3 1/4 Drams Curtis & Harvey’s No. 4 T.S. with a pressure of about 8500 psi.
It was proved with "Proof House (Black) Powder" at about 11,000 psi. Had "E.C." Bulk Smokeless been used for proof, the proof pressure would have been about 18,000 psi.
The pressures in the graph were determined by crushers; add 10-14% for modern transducer numbers