There's a forcing cone just ahead of the chamber. Typically these are not polished by Remington, so they have a somewhat rough looking surface that can look like rings. This does no harm, but it does collect combustion byproducts and plastic from wads easier, and takes more cleaning, which is irksome. It's possible to polish or lengthen the forcing cone then polish. (Don't do this for slugs, though, it ruins accuracy.) It's just a cost shortcut that Remington has taken for over a decade.