http://www.rockislandauction.com/viewitem/aid/65/lid/1139

The Wesson & Leavitt is one of the scarcest revolving rifles made in the US, with no more than 50 made (some sources say only 16). The reason for this is that the Dragoon revolver which Wesson & Leavitt based the rifle on was found to be in violation of several Colt patents. Most importantly, when the Wesson & Leavitt Dragoon was introduced in 1850, Colt had a patent on the feature of having the cylinder index automatically when the hammer is cocked. They filed suit against Wesson & Leavitt, and won the case in 1851, before very many of the revolvers had been made.