8MM/06 I tried the blue wonder thing waste of time and money I needed to refinish a military floor plate ,I call them the company there statement could be the metal on the A3-03,gave up.
I used a guy over in PA called E R Shaw he charges around 85 buck to hot blue and I can say this guy does a great job.
I also have used LMF browning chemical on m/l barrels ,this is a slow rust chemical and takes up to a week to get a great brown finish ,which does't come off.I read the intruction and they do state the browning will turn blue if used in distill boiling water for 20 min: you may want to look into this stuff
here a picture on a t/c Renegade that I buil from a kit flinter