With-out having it in my hands, I'd have to GUESS it was bluing salts bloom.Google 'bluing salts bloom' and you'll learn to stop it. (It happens a LOT on adjustable sights.)If it's severely corroded the base metal, send it back.
With-out having it in my hands, I'd have to GUESS it was bluing salts bloom.
if you can clean it out and not see any marks i would keep the rifle if she shot well