Thanks, the slow brown solution will give the same results as used when the gun was built, to brown or blue a barrel will take anywhere from 3 to 6 passes, maybe more depending on the composition of the steel or iron, each pass creates a layer of loose rust that has to be removed or carded off, a soft brass wire brush or grey scotchbrite pad, more solution then hang up to rust again,usually overnight is good enough then repeat until the desired depth of colour is acheived. Proper degreasing is the absolute key!
I am surprised this stuff is still available really as its proper poisonous, gloves goggles & mask definately a must!