Kevin,
Those surplus John Inglis-made high powders were used extensively by the Canadian Forces.
During it's long service life, there were a couple of hammer, safety, and sear modifications made to issued guns resulting in non-compatibility of mixed parts.
Is it possible that your pistol has the wrong combination of hammer and sear? The mixed up ones I've worked on either would not go on safe, or release when put on safe, or would not reliably fire when cocked. Check the hammer and see if it was "II" stamped on it, indicating this modification. You may have to find some compatible parts to repair it. Did it function properly before you disassembled it?
A another thing to check is the trigger sear linkage that goes from trigger along the frame, up to the slide, and back down to the sear. Any dirt or debris in this area can stop the hammer from releasing when trigger is pulled.
John
