Supposedly, JB Bore Paste is only for cleaning. It works on carbon, plastic, copper and lead, but does nothing to or for the steel barrel.
I have used the Tubb bullets made for reloaders. There are 50 bullets to the box, 10 each in 5 levels of polishing compound. I used them in a Ruger No. 1 in 270 caliber and it cut my groups in half. They went from about 2.5” to 1.25”. It is a chore to clean the barrel thoroughly after each set of 10 rounds, but it gets the job done. You have to start with a super clean barrel, also. You can feel the difference with the cleaning patches as you progress.
I’ve seen it used with the same or better results with an AR in .223. I was so impressed that I bought 6 more boxes for my other calibers, but I haven’t used them yet.
There is a paste for coating your own bullets, much cheaper than Tubbs. It just has three grades of grit (220, 320 and 600). I’m planning to give it a try in a .22 remfire rifle.