Here's an excerpt from this website:
http://www.remingtonsociety.com/rsa/journals/M1882Model 1882 shotguns were never offered as a combination gun or double rifle, as were early Whitmore double guns. Possibly due to manufacturing costs or lack of sales, E. Remington & Sons decided to drop those rare types of double guns. Another reason may be the excessive weight. Of the very few I have had the opportunity to examine, they are awfully heavy guns to carry afield. Instead, Remington offered an auxiliary rifle barrel insert. These were made full length to fit the shotgun barrel, and made with a threaded portion extending beyond the muzzle of the shotgun barrel and held in place by a round nut keeping it centered in the shotgun bore. The inserts contained their own extractors and had an index tab at the rear to insure alignment when removed and replaced. Center fire Black Powder cartridges of the period were available and are so marked on the inserts, Known examples are .38-55 centerfire and .40-70 centerfire. It was stated in the catalogs that, "these barrels are not adapted for high pressure smokeless powder cartridges". Model 1882 shotgun that were originally made for rifle inserts will contain sights secured on the barrel rib the same as the ones found on Whit more combos and double rifles.