i religiously clean all of my guns after every range session. including a dose of Sweets 7.62 copper solvent. every time i get some blue on the patch that i apply it with, and some on the first patch after soaking. and yes, i do know not to use ANYTHING brass for this purpose, or it can lead to a false positive. most of my shooting is done to find the most accurate loads for my hunting rifles. so i want everything possible to be in my favor. but i am curious about how much copper fouling it takes to really screw up accuracy. 10 rounds, 50, 100? i know i have never fired 100 rounds in a row of anything thru any of my rifles, except the rim fires of course. and it has been years since i ran 50 rounds in a row (without cleaning, not all in one shooting string) thru any of my center fire rifles. so i guess i really would not know. back when i did do the 50 round range days, i did not know about copper build up. when i did find out about it, i had my work cut out for me, and i have been very diligent about keeping it at bay since. all of them have well "broken in" barrels. the youngest (a re-barreled 300 win mag) would probably have in the neighborhood of 300-350 rounds thru it. i also know each barrel will foul at a different rate, depending on it roughness, tightness, and velocity. i am not looking for an exact number, just a ball park number.