Cold Finger, I like a few products that take out copper and carbon very well. I mostly get really fouled bores from people that have decided they do not need to clean their bores ever or they just go out and start shooting without Breaking in/Burnishing their bores from the start. my favorite method of cleaning a bore like this is a combination of two cleaners as a 1-2-3 combination. first I will see what I am dealing with by putting a nylon brush on, drenching the bore with Sweet's 7.62 and agitating the sweets every 15 to 20 minutes and then after an hour or maybe as much as 2 hours I will shove a clean patch down the bore. if I get blue, black, and grey I know I am dealing with the trifecta of crud. Copper, Carbon, and Lead. mostly I get blue and black.. the bad boys of copper jacketed bullets. then I use Sweet's 2 more times like I did the first time. if nothing really changes I know I am in for a long hard road.
I will then use regular Hoppe's 9 on a patch with JB Bore paste to mechanically scrub the bore without harming it. if I start getting a copper color out or black and copper I know there is a boat load of copper and carbon.. I clean out the JB and grab for the sweet's if my nose and body can handle more Sweet's. if not, I grab the Wipeout; patch out and accellerator. now I use these products a bit differently than the instructions. first a brush load of Accelerator then a brush load of patch out, at the other end I drip more Patch Out on the brush and pull back through, by this time the whole bore is either foaming or it's staying liquid. liquid is telling me that the bore is just that dirty and it's going to be a long road. I keep agitating the liquid in the bore every 15 to 20 minutes until the liquid is one of these, cobalt blue, midnight blue or too black to tell any other color. then push the nearly gel out of the bore and start all over. IF I start getting just grayish black out of the bore I go to the JB and scrub the hell out of the bore because grayish black is just carbon and needs to be mechanically scrubbed from the bore. I have brought back a 1950's Model 70 from a rebarrel job to shooting 1/2" groups. it can be done. BTW great choice on calibers. the 270 WSM is one of my favorite calibers.