Barrel should be sanded as fine as you want...sand along the length of the part. Some folks say finer than 320 grit is a waste of time...others disagree. Either way, the part needs to be absolutely squeaky clean with not a trace of oil anywhere. A good scrub down with acetone seems to be the norm...handle with gloves only from this point on.
Laurel Mountain Forge makes a barrel brown solution that cuts through a small amount of oil...allowing handling by hand. Good product, and available from Track of the Wolf. Keeping things grease free is still your best bet. When the part is "clean", water will not bead but rather sheet off.
The rust bluing solution is applied to the surface with a bit cotton rag (what I use) VERY sparingly...just enough to dampen the surface, it should not run.
Then it is allowed to form a layer of rust. Some folks hang the pieces in a room with higher humidity (bathroom), some folks use a humidity box. Once the surface has a coating of red iron oxide, it's time to convert that red iron oxide to black iron oxide.
I use a vertical conversion tank. With barrels, I plug the muzzle and suspend the barrel from the breech end. I don't boil the parts per se...I boil the distilled water in a kettle and pour it into a piece of 2" abs pipe with a cap cemented on to it. Insert the barrel leaving the transfer port still out of the water and leave it a few minutes.
A good idea to make sure the kettle holds enough water to fill the pipe.
Pull the part out and dry it off..let cool slightly...it'll be black now if all is well. Card off the loose black iron oxide with a piece of old denim or DEGREASED 0000 steel wool...rub HARD. Take as much off as you can.
Repeat the process, maintaining faith.(the hard part) The color will deepen with repeated cycles...usually takes 3 cycles before it's easy to see. Keep going...I usually end up doing 12 cycles.
When you've reached a point where you're happy with the color, give the barrel a good scrub down with baking soda and hot tap water...then dry.
While the barrel is still hot, rub it down with a good paste wax...let it dry. Buff the heck out of it, re apply the wax and buff it again. Don't need power equipment, elbow grease is adequate. The wax will fill any open pores in the finish and add a bit of shine. Doesn't show finger prints either.
Small note, as I do things, from the transfer port to the breech end of the barrel does not get blued...I do not apply solution there either. Not an issue for me when it's hidden by the receiver.
A pretty basic rundown, but should give you some idea of the process. Suggest doing some research and playing with a piece of scrap or such first.
For a trial effort, you can make a rusting solution consisting of: 2oz 3% hydrogen peroxide, 1/4tsp white household vinegar and as much sea salt as will dissolve into the solution. This solution works quite well on most steels I've tried it on...not so well on 4130.
but I thought oil are use instead of water now."yay, me wanna make big multishot pnoob with 1000 psi foot pump compressor using diamond as main material. Do you think wet bread make good sealant? "
