It's common for factory and standard service rifle barrels to scrape jacket material off the first few bullets. After the micro pits and grooves are full of copper, no more's washed off and they shoot decent. Bullets with jacket material wiped off are unbalanced; they don't shoot accurate.
Top quality match barrels won't do that; they shoot to point of aim starting with the first shot and do so for hundreds of rounds thereafter.
Leave that copper in the barrel; it won't hurt anything. Just do simple cleaning and nobody will know about it and your rifle will shoot well thereafter.
US Navy Distinguished Marksman Badge 153
Former US Navy & Palma Rifle Team Member
NRA High Power Master & Long Range High Master
NRA Smallbore Prone Master