Ah yes....the Roper revolving shotgun...yeah I have heard of it, and have seen a few pictures, but I do not have alot of info on it.
It was patented in 1866 by Sylvester Roper of Amherst, Massachusetts. The 4-shot repeater was built by Roper in Amherst until 1867 production then moved to Hartford and production continued from 1869 thru 1876. Although production figures are unkown, it appears that it has certain rarity. It appears to have had a fragile action resulting in malfuntions during hard use. The Roper revolving shotgun was the first repeating shotgun. I personally have only heard of them chambered in 12 ga. and 16 ga., however other gauges may certainly have been available.
Roper himself was quite an inventor and a builder of steam motorcycles and automobiles. In 1868 Roper patented the first removable choke system, though this design faded into obscurity along with his revolving shotgun. Roper died in 1896 while demonstrating one of his cycles. That motorcycle resides in the Smithsonian.
Here is a picture from my website of the Roper Action: