There were two versions of bullets for the Smith carbine (and the Gallagher carbine). The version which had a very thick raised band encircling the lead bullet's body fit into a rubber case, and is called the "Smith Waterproof" (due to the rubber case). The other version, which you found, lacked the "waterproof" version's prominent band, and fit into a Poultney's Patented paper-&-foil case.
The "Waterproof Case" version fit only into the Smith carbine. Your version could fit into either the Smith carbine or the Gallagher carbine.