From what i have been able to determine fromLee Kennett's article in the '75 Gun Digest my new to me boxlock was given a definative proof 11.6 grams of powder and47.3 grams of shot to get a proof load of 12,800 PSI . the service load is 5.8 Grams of powder and35.5 grams of shot. It is a 65mm chamber. If I converted the grams to ounces correctly it is a 1 1/4 oz load of shot. does anyone have an educated guess about what pressure the service load would be?