Affordable bore scopes are a recent development and I would guess that whoever owned your .223 before you did not have a clue about the hard carbon in the barrel. Given that he did not know he had the problem, it would be logical for him to have used the usual combination of one or more solvents, patches and probably bronze brushes, although there has been enough bullshit on the internet about bronze brushes and imagined damage that the brushes may have been nylon, which would have exacerbated the problem. What this adds up to is that the stuff that you labored so hard to remove was the result of hard carbon being deposited and piling up from the first round. Now that you have removed all of that, periodic use of a suitable abrasive cleaner should keep you ahead of the problem. For this kind of work I have had good luck with the judicious use or IOSSO paste, and more recently have switched to a different form of the same material, Thorroclean and Thorroflush. My routine for these is to do a thorough cleaning including bronze brusing and patching with solvent to get down to the hard stuff. At that point I use the Thorroclean and Thorroflush, or previously IOSSO paste. My methods of application have worked very well for me, and I am meticulous with my rod work and cleaning all of it out of the barrel, off of the rod and out of the rod guide. For the IOSSO, following a procedure that I read in an interview of Tony Boyer, I use a regular black nylon bore brush, not the hard kind but the softer variety.
I fill the bristles full with the IOSSO and short stroke it, starting in the throat and working foreward with short strokes, covering the area that the bores scope showed me had hard carbon. Do not use the IOSSO turning black as an indicator. It will turn in a clean barre. For the new user, I suggest doing some experimentation by cleaning some, patching it out, and then taking a look with your bore scope. Doing this you will soon arrive at how much work with the IOSSO is needed for a given powder, caliber, and round count. I take a just enough to get the job done approach. For the Thorroclean I do something slightly different than the instructions on the bottle. For 6mm, I wrap one of the same type nylon brushes with a 1 3/8" square patch and apply the Thorroclean from the bottle, evening it out with my finger tip. There is a trick to applying the Thorroflush to a patch. It wants to bead and run off. I have found that it does a superior job of removing the Thorroclean but it irritates my skin so I simply put on some closely fitting 6 mil. disposable mechanics gloves. The trick is to let the Thorroclean wick into the patch without any pressure on the bottle, and to quit before it starts running off. I prefer the new products to IOSSO but they both do an excellent job on hard carbon. I find that if you clean regularly and thoroughly that hard carbon is manageable without too much trouble.
