Care to elaborate on your cleaning routine with abrasives?
The way that I used IOSSO for many years still works. It came from an interview of Tony Boyer that was published in Precision Shooting Magazine. AT the time, Tony was still shooting T powder, which I believe was prone to making hard carbon.
He would do this after every match (five shots for record and however many sighters). After a regular solvent brush and patches cleaning, he would use a nylon brush completely filled with IOSSO in the back of the barrel, the back 8-10 inches. He would work on the throat and then work forward, after which he would carefully patch it out. I personally use a lot of patches and solvent to make sure it is all removed. I am sure that he did the same.
Given that IOSSO will blacken in a clean bore, and that I would use up quite a bit if I cleaned the brush, I started wrapping the brush with a little aluminum foil after each use, leaving whatever IOSSO remained on it, and adding as needed the next time.
Since I was not using T powder for my 6PPC, and since 133 did not seem to create a hard carbon problem, given the frequency with which I cleaned my PPC barrels, I hardly ever used any abrasive in them, but for other calibers, mostly varmint, using other powders I would use IOSSO, infrequently, on an as needed basis, based on inspection.
A few months back, since I had run out of IOSSO, I decided to try the Thorroclean, Thorroflush combination that Bullet Central sells, which is IOSSO based, but as a liquid. I like it a lot. My method with it involves wrapping one of the softer black nylon brushes with a 1 3/8" square patch and applying the Thorro clean to it. Back when Tony did the interview, harder nylon brushes were not available, so I use and recommend the slightly softer black ones for his method. The Thorroflush is used per directions and does an excellent job of removing the Thorroflush, although it can irritate the skin of my hands. For that reason, when usijng that combination, I put on some disposable mechanics gloves that I purchased a quantity of some years back.
I should add that I would never use a bronze brush with any abrasive cleaner.