I hung my shotgun barrels from a rafter in my garage, and then heated the barrels with a propane torch from the bottom( muzzles) on up. Since heat rises, this method gives a benefit of allowing the escaping( rising) heat from the first area heated to begin to heat the areas above. I applied the Plum Brown solution with cotton, but any clean rag will do. I did 6-8 inches sections of the barrel at a time, working my way around the barrels, and then working the second barrel the same way, It did not take much sweeping of the flame of my propane torch over the steel to keep the barrels hot, as I worked my way from bottom up to the tang. Degrease the metal surfaces well, before applying the solution, and remember to not touch the metal with any skin, as it will leave both oils and salts on the barrel, that prevent the product from contacting the metal. When in doubt, heat the metal in a given area again, and hit it with more solution.
I had some "slag" in one of my barrels, and I ended up heating that portion of the barrel up much hotter than 275 Degrees F. to finally get the solution to brown that area of the barrel. I have no idea what the slag was, but I would have to point out the area on that barrel where its located for you to see it has a different" texture" to the finish there.
I will have to buy another bottle of B/C Plum Brown, and read its instructions again. I did not know that it was a "hot brown", as others have said here. I bought three different browning products at the time I bought the B/C Plum Brown. I tried them all and wasn't impressed with the others.
I stand corrected. Thanks to Zonie, and others. :hatsoff: