Good point on the choke markings and age. No references with me but wasn't the gauge and choke in a diamond after 1875? I thought a barrel without choke was marked with the gauge in a diamond. This is simply marked 8 on both sides.
The pinfire thing may be true but other pictures of the top of the breech don't seem to show any indication. Also, when did the underlever come into use? I thought the number was around 1859, after which I suspect pinfire production may have been low. I will say a conversion in 1897 or later would explain the W&S mark, but that seems awfully late for such a conversion.
