Sweets 7.62 will remove copper fouling if used regularly. However, it sounds like your gun may need something stronger to begin with. Outers makes a kit for this called "foul out". It is an electro chemical process. It also sounds to me like you have a problem with the bedding or perhaps the bolt lockup on your rifle. Shot stringing is the telltale sign of these problems, that, or you are shooting it way too fast and heating the barrel up. Rifles shoudn't shoot "patterns", the should shoot groups.