Fire bluing, or 'Nitre blue'?

[lugerholsterrepair]

I have used a small propane plumbers torch for many gun parts...Strawing and fire bluing. I very nice result can be achieved if you pay attention. I clean the parts very well with alchohol and lay them on a clean soft firebrick. Run the torch over the part and you can watch it turn colors. Be careful not to over focus the flame directly on the small part. Slow and steady. Take the flame off earlier than you think..the part will continue heating with the flame off and sometimes get darker than you want.
I don't know about larger parts like frames and cylinders..I never tried any of those. You might want to try a toaster oven
for larger parts for a more controlled heat.