"Long Tom" was a registered trade mark of Sears Robuck Co. The Long Tom was made by the Cresent Firearms Co. until 1930. The Stevens Arms and Cycle made these until the mid 1940s. One of these sold on GunsAmerica for $300 dollars in very good condition and a it was a late Nitro safe Mdl.
Well, your shotgun came from Sears. As did a LOT of guns back then. From 1905 to 1915, a Sears wholly owned business called Meriden (not Meridian as it is often misspelled) made the Long Tom for Sears & Roebuck. After 1915, and up into sometime in the 30s, they were made by the J. Stevens Arms and Tool Company.
Your Long Tom was probably made for smokeless powder, HOWEVER- the length of shotshells was not always 2 and 3 quarters- and 100 years IS getting old. Please understand that just because an unfired shell will FIT, does not mean it is safe to shoot. Modern shells have a crimp that must have room to unfold- where the ALL brass shells did not.
Unless the zombies have chewed their way thru the front door, and all your other guns are inoperative, i would leave the Long Tom hanging in a place of honor.
PS- there are reprints of the early Sears Catalogs you may get thru your local library. The Long Tom is not is the 1896 catalog (a lot of other guns are, tho) but I THINK it may be in the 1906 catalog.