I just read a post where someone stated that the Cadet had never been intended for black powder. I had always assumed that the chamber marking of .310-12-120 referred to a loading containing 12 gr of black powder behind a 120 gr bullet. What kind of smokeless powder would take 12 grains to give a velocity of 1200fps? Cordite? I didn't think that the case had enough volume to take 12 grains of any modern smokeless powder.
(And why does the number 12 figure in the powder charge, bullet weight and muzzle velocity!)