Not an expert on JB Bore Paste, as I've only used it once. I used the Bore Bright and Polish versions to help clean a really badly copper fouled rifle barrel recently.

In my opinion it worked well, there was an obvious smoothness in running patches through the barrel after using it. To remove copper? I still think Barnes CR-10 worked better but using the paste definitely reduced the total time to get all the copper out.

I didn't notice any harm to the barrel, but again I do not have a bore scope to be 100% sure.

340,