I have owned more probably more than my fair share of Contender barrels over the years and have never seen any factory production barrels that had a brass ring on them. I have seen a few that had been after market modified by threading the end for a removable muzzle break and/or silencer (where legal of course). Brass thread protectors are not uncommon to protect the threads when what ever was screwed on the end is not installed. Does your brass ring screw off by chance?
Mike