The 1855 “Root” pocket revolver was a reasonably successful design for the Colt company, although it was not the best mechanical design. The side hammer design used the cylinder axis to rotate and lock in place instead of using the rear face of the cylinder, which resulted in several small and delicate parts. In an effort to correct these deficiencies, Colt and his factory superintendent Elisha Root experimented with a “zig-zag” design as well, which would use and external cam running in grooves on the cylinder wall to rotate and lock it. Root received a patent (#13,999) for a system using a ring trigger and lug on the bottom of the frame, and these two prototype revolvers demonstrate a similar system with the lug on the top of the frame. This system was not ultimately adopted, and these remain just an interesting look into the experimental workings of the Colt company.
Colt Sidehammer Dragoon: https://www.full30.com/video/93143ad302e5d2ef291f351f4fb40e0b
Colt 1855 Revolving Shotgun: https://www.full30.com/video/cef8c4a5ca4e08559aa6494dccd38030
Mauser 1878 Zig-Zag Revolver: https://www.full30.com/video/1f5255d06a679679eb78c7da923fbfb5