devildoc,
Since I was the one who posted Gale McMillian's opinion, I will answer your question. I dont know if anything is wrong with JB's. Many people feel that it being an abrasive will do more than just clean, it will actually remove metal from the bore. McMillian's objection was that when it was used on a patch, especially, that tolerances couldn't be maintained and you really have no idea how much metal you may be removing. I am no expert on this. I have used it, but I will only use it now for extreme cases of fouling. I would never use for barrel break-in. As for Coppermelt vs. Sweets, one could say that Coppermelt is Sweet's on steroids! So is Montana Extreme 50BMG. Lots of ammonia to chemically remove the copper. Didn't mean to rock your boat, just another example of the number of different opinions that are out here. If you are happy using JB's, please dont let me stop you. Good luck and good shooting,
Jim