From the new photos its obvious that the lock fence is not tight against the barrel. That may just be a function of the lock not being inletted deeply enough into the mortice, possibly just the mainspring causing the interference. With the lock tight against the barrel, powder cannot leak out into the lock recess, and I'm sure that is where most of the powder is going. That needs corrected!!! It will prevent powder loss, and potential damage to the stock from the leaked powder igniting in the lock recess. Likewise, with the lock tight against the barrel, ignition will improve.
Once that is corrected, I would recommend laying a bead of JB Weld around the top the the pan and filing it flat to further seal the pan/frzzen. Ideally, tig weld would be better.