I am an English trained gunmaker (Ret) so I have extensive training and experience with proof processes. Your method is sort of a unique take on how it is done and it certainly works. However, a proofing is done with an "over-charge". If you are going to load 50 grains then this might be a "proof". Explained crudely, the proof load is twice the maximum amount of powder you would normally use. Nowadays with technology it is essentially twice the maximum pressure you would get from the most "powerful" commonly available load. I would think with that gun you would load somewhere around 70 or 80 grains of powder. With that in mind, you have neither a "double-charge" nor a "double-pressure" load that you tested with. I appreciate your enthusiasm and I like your ingenuity! I am not convinced that barrel is perfectly safe with that one blast. I'd like to see it work out for you, so be careful and somewhat reserved as you proceed.