I agree on https://www.midwayusa.com/product/2...2-copper-remover-bore-cleaning-solvent-liquid. This stuff works Great. Not sure how it can work so well with out a heavy ammonia smell,but it does. Wet patch 5 or 6 times and let set for how ever long you have time for and then wet patch 5 or 6 more and copper is usually gone. I always let my rifle soak with the barrel pointing downward resting against the inside corner wall so as not to fall over. Also a little trick that I use is to set the end of the barrel into a Dixie cup with some round cotton pads to protect the crown and soak up the blue solvent as it runs down and out the barrel. I feel this method works well as far as keeping the solvent contained and letting it run down the lands and groves. The bottle even says that it's a rust preventive and can leave it in the barrel until you are ready to shoot again, but dry patch before firing. That's why I say leave it in for as long as you want. It still works great with fast cleaning, but if I don't have time at the range to clean I take my time at home the next day letting usually 3-4 rifles soak over night. Also you do need to use aluminum jags and nylon brushes so as not to get a false reading.
I've also used Holland's witches brew with his cleaning instructions. It works good but the Bore Tech Cu+2 copper remover just seems to work a little better easier. Just my 2 cents worth and to some it's not even worth that. Good luck and have fun!!