I've been doing a lot of shooting (load workups for my 260), and I've tried quite a few combinations of cleaning solvents to see what worked best or worst. Keep in mind that I don't have everything that the market offers, but I do have quite a few. So here's what I think that I know:
Best. Slip2000 Carbon Killer, followed by the Boretech Eliminator
Almost as good. Butch's Boreshine or Shooter's Choice, followed by the Boretech.
Wrong order. The Boretech, followed by the Slip2000 Carbon Killer.
Summary. Without a doubt, the Boretech Eliminator is the best Copper remover I've ever used. The Carbon Killer is excellent, but I"m not going to say it's the absolute best in my experience. It probably is.
Some more of what I THINK that I've found, is that just maybe you don't want to remove all of the copper every time you clean the bore. My best accuracy appeared to be after I used the Carbon Killer and the Boretech Eliminator to clean the bore down to the steel and then after I shot 10 or 12 rounds I cleaned with only the Butch's Boreshine. That's when I got the best groups, though maybe that was just accidental. I just don't know for sure, but I am wondering if maybe it's best that the bore does have some copper. I wonder what the extreme accuracy shooters would say about wanting a little copper in the bore or no copper at all. Probably it would depend on the individual barrel and maybe even to some degree whether it was button rifled, cut rifled, or hammer forged. All this heavy thinking is way over my pay grade but I have always been, and remain, an inquisitive Engineer.