...I don't know what pressure the gun was "designed" to shoot...
If the gun is Belgian;
Law of 1893 - Obligatory Proof of joined barrels of multi-barreled Breech loaders and Muzzle loaders
24 gauge
14.6mm Bore Diameter
7 grams Powder Charge
16 grams Shot Charge
Law of 1924 - Definitive Black Powder Proof of Breech loading Shotguns
24 gauge
70mm Maximum Chamber Length
6.8 grams Powder Charge
30.7 grams Shot Charge
The Belgian Proof house dramatically increased the pressures by 1924. They were at least 80% over the service load.
Pete
