The round or roller part catches onto the ejector/extractor and helps in both the opening and closing of the breech. Like Mark has stated you will get used to it and enjoy it's feature. It was discontinued in 1899.
I collect serial numbers for the older Syracuse and later Hunter Arms hammer guns, and it you could give me the whole serial number, gauge, grade, barrel length I would appreciate it.
Also does yours have L.C. Smith Syracuse, N.Y. on the top of the barrels? Most at this time did not have a maker's name on the barrels.