Once a rifle has been shot considerably, you will not get 100% of the cooper out of the bore. The Outer's Foul Out kit will get almost all fouling and copper out.

What I would do is get some J-B Bore Cleaning Compound and Sweets 7.62mm Cooper Solvennt. I would saturate the bore with the Sweets, apply the J-B to a tight fitting bore patch, then run the patch up & down the bore for 25-50 strokes. Then re-saturate the bore with Sweets and run a dozen or so wet patches down the bore, then brush scrub the bore for several strokes, wet patch the bore some with Sweets, then dry patch. By this time you should see a dramatic difference in the bore it self and your patches should be much cleaner.

You do not want to use J-B compound every time you clean the bore, because it is a mild abrasive compound. But you can use every couple or few hundred round, when the fouling builds up enough to warrent it's use.