I don't know why Oscar disliked the Brownells Nitre salts,,but he really had it in for them, or for Brownells.
I've found the salts to work just fine. You can also boost the temp to 850/875F and get a deep blue-black also, just as with Sodium or Potassium Nitrate.
Most any metalic salt can be used. It melts and is reasonably clear so you can see the part(s) in the stuff.
The temp does the bluing w/o the atmosphere O2 interfering.
You can use molten lead too as long as you get it to the right temp.
Manganese Dioxide is mentioned in the original Winchester write-up recipe for Nitre bluing as an added ingredient.
The hand written notes are shown in Midas' book on Winchesters,,if you have a copy of that.
I don't recall the %, or if it even says how much.
Others much smarter than I have said it was to lower the melting point of the concoction once mixed.
I guess that'd make sense if you wanted to use it for different tempering levels and colors.
I don't know.
I've just used straight Sodium Nitrate, Potasium Nitrate, even Ammonium Nitrate in the past and gotten the desired results.
The Brownells salts works fine for me now.
I still use lead to draw the temper on springs.
Be careful with any of this stuff,,eye, face and cover gear a necessity. Use a sturdy set up,& keep the kids and pets away.
