I actually originally wrote the bones to this article about three years ago, mostly in response to a Propnomicon post about a cased prop Watson gun, but let the article languish uncompleted. Once I came back to the subject, I found that a few others had attempted to figure out the Watson gun question, so I decided to polish up the article and publish it finally. I had intended to also produce a second Holmsean weapons article about the air gun used by Col Moran in the Adventure of the Empty House, but it didn’t go much beyond the outline stage. Hopefully I’ll get that article put together.
You can also Google the manufacturers Flobert and Remington for examples.