Glenn, I bluing barrels in my garage and unfortunatly in winter it's allmost impossible to get boiling water in tank on 2-burner propane camp stove. However boiling tea kettle works just fine for me.
I just finished bluing barrels for my .577 DR project and funny rusting solution I used consisted of 2 componets only (CuSO4 + HNO3), but bright black color I got was just fine


Geno.