I'd have to re-read Kennett's article, but first considering gauge, I wouldn't venture over 9k psi and the service load stamped on the tubes I've seen on pre-1912 16 bore doubles was 2.2 grams. I'd say the German's "square" load is just under or right at 1 ounce. 1 1/4 oz is going to rattle your teeth in most pre-WWII German sporting arms.

Kind Regards,

Raimey
rse