J&B Bore Cleaner is good stuff, but I suspect that this barrel will be far too gone for it to do much good. It all depends on how long the barrel has been left in this condition, and how humid was the area where the barrel was stored. It certainly will clean up the bore, so that all the bad pits can be located, however.
I like to put a 3 inch square cleaning patch(or two) on the front of a bore brush, and then heavily coat it with Bore Cleaner. Fix the brush to a rod, and put the other end of the rod in a hand drill. Go at it. The Bristles of the bore brush will hold onto the cleaning patch so that you can go back and forth with the polishing brush, and not worry about losing the Cleaning patches.
You have to change the patch several times, with new bore Cleaner on each patch, but it will smooth a bore, and put a good shine to it.
It is a VERY fine abrasive polishing compound, so its a waste of the stuff to use it on a badly rusted bore, until you have honed the metal down the point where this polishing medium can make a different. Otherwise, you find your self polishing TOOL marks, in the bore, rather than finishing the bore itself. :shocked2: :nono: :surrender: :thumbsup:
If you are going to resurrect a bore, take your time, and go through the grits, from coarse to very fine, so that you end up with a polished bore. The smoother the bore, the less residue "sticks" to it.
If you grease the bore AFTER the load is seated, I find that there is very little residue that sticks to the bore, and its easily cleaned out by running a lightly dampened Cleaning patch down the barrel and back out again. On humid days, run a second and sometimes a third DRY cleaning patch to dry the bore before putting the next load of powder down the barrel. Examine the dry patch when it comes out of the muzzle. If its very greasy looking, run another patch down the barrel. That patches will tell you when you need to ADD to your loading procedure, and, conversely, when you don't have to change the procedure when shooting in arid conditions.(ie. Low humidity, or very cold, below freezing temperatures.) :hatsoff: