I get that on my barrels also and I soak mine in hoppe's once every 10 times I take the guns to the range. What I've noticed is it depends on what bullet you use, certain ones leave that copper line, some don't.
i get that in my 1911s, xdm's, berettas i use a lot of plated bullets and non plated bullets i got that on my lcp from using factory SD ammo too. doesnt affect accuracy or performance.
"Gun control: The theory that a woman found dead in an alley, raped and strangled with her panty hose, is somehow morally superior to a woman explaining to police how her attacker got that fatal bullet wound." L. Neil Smith
The problem with being stupid is you cannot simply decide to stop doing dumb things...