I just finished my second and third shotguns done by rust bluing. My first was a single barrel junker which rusted nicely with LMF, and I scratched it between six or seven passes. I was not then equiped with boiling pans and tried to steam it to convert in a vertical PCV pipe. Water droplets condensed and ran down the barrel producing an array of psychedlic striped colors. Too much steam I guess, but the finish I got was deep and lustrous.
Two very pitted guns were next attempted...a Dynamite Nobel 16 pump apparently made with a lower alloy steel than the Browning Citori which was its bath tub mate.
I used Plinkingtons Classic Rust Blue from Brownell which is a match to their own by the same name I am told. I draw filed and finished to about 320 and next time will try 220 as the result was just right for the Citori but a little too bright for the cheaper gun. The lower alloy 16 ga. frame and barrel behaved much more like the instruction said they would....very good result.
The Plinkingtons was easy to apply with a two inch make up pad wrung out well. A quarter reaspoon in a clean small gass vessel reduces contamination. One pad would absorb all of the agent, and I just turned it as I went. Two hours later a second coat was applied. One hour later i boiled in a stainless tank.
The first boiling produced fine black soot on each gun but the Citori showed a circular pattern from the gas flame port of the burner. I then switched to scalding with boiling distilled water which worked fine for the low alloy pump gun.
The Citori began to show a coppery sheen by the eighth pass and the rust scratched off was not converted. Two more and it was worse. One more pass and I then boiled it for a half hour which gave a good full depth conversion to black.
Ten minutes in scalding water was not enough, and I would recommend longer than ten minutes and boiling if you can. A sheet metal shop can build your tanks....4 or 5 inches wide is enough and takes less distilled water.
I liked not having to heat the barrels. I degreased by overnight in premium gas and boiling in Dawn dish water. rinsed with hot soft tap water. Next time I'll try Simple Green cause the gasoline in that quantity is hard to safely burn. The only oil problem that I had was I forgot to degrease the wire that I suspended the barrels in. One spot only, but still visible after ten passes.
The plugs were holding me back, but were easy enough to make with a one inch belt sander. I used soft dowels and they came in handy to use as handles. Neither the agent or the boiling water caused any trouble with the bores or internal parts. They cleaned up easily.
I am going to look into some sort of tube burner or a double boiler to heat the water a little faster.
I only waited twelve hours after the final treatment, pand used Outers gun oil applied twice and rubbed in the next morning with paper shop towel, followed by wax. Next time I will use boiled linseed oil before the gun oil just to see any difference, and give more time to age the finish beforehand.
Fun projects but had thirty hours of attention on those two badly rusted guns. The Citori owner was happy enough to hand me all of the cash in his wallet.....450, which covered my expenses nicely. Keep an eye on everything....use a lot of nitril gloves and don't get in a hurry....you'll be fine.