Ah, very interesting but two of the old guns I'm bluing at the moment have cylinders which are sealed to the breechblock with solder and I'd be loathe to go anywhere near them with a blowlamp.
Besides which I seem to have cracked the job by switching from acid fume bluing to rust bluing using Ammonium Chloride --- I managed three rustings today.
One of the items I'm bluing is the barrel weight for this rotary pistoned HW35 which should finish the front end off nicely.
All the best Mick