Here is a barrel that is being rust blued and the only place that I plugged is the touch hole and nowhere else. Do not coat the bore with ANYTHING or you very well will contaminate your barrel browning/bluing job. I applied three coats of Mark Lee Express Blue to this barrel with three immersions in the hot water bath then removed the barrel and wiped and dried off the water. I swabbed out the bore like when you clean the barrel after a day at the range and gave it a good dose of rust protectant. The next day I wipe it down again - swab out the bore and give it another dose of rust protectant. I do this for about 5 days and then assemble the rifle and I am done. I will check on its progress (flash rust) for the next few weeks. This is not a difficult job. Below is my normal process that I most often use.
First let me say that there are other ways to accomplish this task and get very good results but I find this works for me.
Mark Lee #1 Express Blue, small glass container, tap water (I have a water softening system in the house), Coarse cloth such as heavy denim, terry cloth towel, or maybe burlap which I have not tried, rubber/ nitrile gloves, heat source to heat up the water to boiling or a little less and a degreaser. any soft cotton type applicator pads.
I use a length of steel gutter from Home Depot that I solder on end caps to contain water. I suggest making the gutter length 2 to 4 inches longer than your barrel plus tang.
Bend up some stiff wire – I use hardware store balling wire to support the barrel at each end in the gutter so that it does not contact the bottom. NOTE: if rust bluing a lock or small parts I use a small disposable aluminum “loaf pan” and just put the parts into the water without trying to support the parts off the bottom – the bluing comes out fine - might also work for a barrel but I have not tried it.
OK – now for the barrel preps. What I will be discussing here is what I did for this barrel and for the finish results I was looking for which was a dark blue/black non-polished look which is what I do the most of.
I block sand with both 220 & 320 grit wet/dry paper. I did not try to remove all surface marks just to “knock down” heavy machine marks. You could draw file before doing the sanding if needed. When done you want to degrease the barrel good - I used acetone. Wear some kind of rubber/ nitrile gloves so you don’t leave fingerprints or finger oils. I made up a barrel holder from scrap wood so that I could apply the Mark Lee #1 Express Blue.
I plugged the touch hole, my breach plug was already installed. I slipped the barrel into the barrel support and put on my rubber/ nitrile gloves. I degreased the barrel again. I poured a small amount of the bluing into a small glass container and dipped my cotton pad into it – squeezed out most of the excess and starting from one of the barrel made a continuous pass towards the other end of the barrel. I did the same with the other 7 flats. NOTE: reapply the bluing solution to the pad to keep it slightly wet but not “dripping” wet you don’t want any solution pudding on the barrel. When completed set aside for an hour. After the hour I reapplied the bluing solution as above and set it aside for another hour. I did this process two more times.
I placed the gutter over the two gas burners of my kitchen stove and filled it with tap water enough to cover the barrel I placed the stiff wire supports for the barrel that I previously bent to shape into both ends of the gutter. Turn on the gas to high. When the water is hot I place the barrel into the water and leave it there for 10 to 15 minutes. Removed the barrel (be sure you have your rubber/ nitrile gloves on – also the barrel WILL be HOT), reapplied the bluing solution with a new pad do not “puddle” the solution on the barrel. Replace the barrel into the hot water for another 10 to 15 minutes. Remove the barrel and take your course cloth and buff the heck out of the barrel (1 or 2 minutes). Do this process for another two or three times. That’s it – hope it works out like you want – does for me.