FloridaFialaFan,
The Model of 1891's are some of my favorite Smith & Wesson's. There were approximately 862 of the Single Shots manufactured in 22.LR, 229 in .32 S&W, and 160 in .38 S&W. That being said, these single shots also share the same serial number range as the .38 Third Model Single Action Revolver, so it's hard to know exactly how many were produced in single shot, as they seem to be more available than the .38 Single Action Revolvers, of which there were supposedly a much larger number produced. I don't know how much knowledge you have of the '91's, but the single shots were made on the same frame as the .38 Single Action 3rd Model Revolver, and you could replace the cylinder and barrel of the revolver with the single shot barrels. That's why your single shot frame has the recoil shield present. On the 2nd and 3rd Model Single Shots, the recoil shield is no longer used. There were also a small number of sets (app. 92) produced that featured the .38 Single Action 3rd Model revolver along with a matched number Single Shot barrel. As previously mentioned, these Single Shots were produced in either .22 LR, .32 S&W or .38 S&W in 6", 8", or 10" barrels, with the most common configuration being .22 LR with a 10" barrel. They are an interesting firearm and one that you don't run across every day. Enjoy it and I hope this information was useful. By the way, I got my numbers out of the Standard Catalog of Smith & Wesson by Jim Supica, a must have book for S&W collectors.