When I found out that Boretech Eliminator was great for copper removal, I got some and used it. Yes, it's good stuff and I took all the copper out of most of my rifles. Then I found that a couple of them (not all of them) weren't shooting quite as well. So I shot em a while and then used Butch's Bore Shine for cleaning, which left some copper in the bore, and I got my accuracy back. Based on that accidental experiment, it does appear that some rifles need some amount of copper in the bore to shoot their best. That is what I presently think, though I honestly do not absolutely know that to be the truth. If I'm wrong, at least I'm comfortable in my ignorance.
And don't bother with the Sweets. If you want the copper out, the Boretech Eliminator will do it for ya. I hear that the KG-12 is even better, but I haven't tried it. Haven't needed it.