Even if you still have copper in the bore it does not mean the gun won't shoot fine and I don't really believe you have to get every last nth out of it either on the other hand you may have a bad spot in the barrel that has a lot of it there and removing the copper from that spot may help. I notice shooting my 7 mags that they for whatever reason fould up pretty good and the group size does increase. I usually use the Foul out III on all the guns at least once a year and those bores are clean when that thing is done and I don't have to breathe in all those chemicals. If you don't have a Foul out unit just make a fixture that will hold your rifle vertically plug up the muzzle with a rubber plug and pour in CR-10 or Sweets with a funnel and let it sit there for 10 minutes...that should do the job pretty darn well also.