Frizzens with rollers seem [to me at least] to be somewhat "splattered" across the years, without a clear time span. They appeared to be a superior design when compared to the more common frizzen spring roller that eventually wore a "dent" in the roller from contacting the small, rounded foot of the frizzen in the same spot all the time, eventually making its action less smooth. With the roller on the foot of the frizzen, it rolled against a flat, smooth surface, keeping the roller round in shape, and a smoother action for a longer period. Perhaps it was a cost factor vs. the frizzen spring roller, but it's hard to see how that made much difference in lock construction costs.
Shelby Gallien