Having been the purchaser
Of several military surplus rifles over the past few years, I'm REAL familiar with copper fouling....Suspect some of the "worst" ones I've gotten had many hundreds of rounds poured through them without cleaning. I sporterized one of the Mausers I bought, and I spent untold HOURS with the regular Hoppe's Benchrest-9 Copper Solvent, and was STILL getting green-blue patches out of it (although it shot pretty well)....Then my buddy and I were in a gunshop, and however the subject came up, the gunshop guy mentioned the new foaming bore cleaners.... He gave us a partial can (Nice Guy) of the Gunslick (as I remember, I've tossed it now) brand. Soooooooo....I tried it out on FrankenMauser as follows: I'd stick the tube into the action with the barrel at a very slight downward slant to the muzzle (1st lesson: make sure its TIGHT into the chamber/bore...It comes out VERY forcefully and will end up all over the action/stock etc.!!!!)....Gave it a good squirt, till I saw it come out the muzzle...Let it sit for 5-10 minutes, give it another squirt...Did this quite a few times, until foam started coming out white instead of blue. Finally ran a couple patches through to clean out the residue...AND, much to my amazement the bore was absolutely mirror, shiny bright...No scrubbing, no (potential)cleaning rod or Brush wear..... SIMPLY AMAZING!!!!
Now the more amazing part....NO ONE (including the place we got it from) carries this stuff in my area (any brand)...He just had the one can, given to him by the salesman....So I guess its mail-order only, for now. But its well worth the cost. But I used a ton of it on this one gun, on a normal gun with less fouling it would probably last a very long time.
Any way, this stuff is GREAT, so I would give it a try...I left some of it in the barrel for quite a long time (total maybe 3-4 hours) and it didn't seem to hurt anything (although I don't have a borescope to look for microscopic damage) and the gun shoots as good or better than before.