After noticing a drop in accuracy and actually seeing copper in the lands of the barrel I decided to de-copper my R51 barrel. Cleaned barrel as normal with M-Pro 7 cleaner. Then ran a wet patch of 91% rubbing alcohol thru barrel. Then a wet patch of Sweets 7.62, let sit for only 5 minutes (it is ammonia based) and ran a dry patch thru as directions stated. Dry patch came out blue (copper). Did same process a couple more times, until dry patch came out clean. Then I re-cleaned the bore with M-Pro7 gun cleaner. Do not let Sweets sit in barrel for more than 15 minutes or it will eat your barrel. I used this on all of my match rifles (I am a Master rating in NRA High-Power shooting). Sweets is the only product that "really" gets the copper out. Then a patch with a light coating of M-Pro 7 gun oil I push thru bore. A clean barrel and gun with good lubrication is a happy gun that will perform reliably when required!! Please clean your magazines after each shooting session as well. A firearm is only as reliable as the magazine that is attached to it