http://www.rockislandauction.com/viewitem/aid/65/lid/1091

Sylvester Roper is not a well known name in firearms history today, but he made a number of notable contributions to the field - in addition to his work with motorcycles and automobiles where he is much better remembered.

The Roper revolving shotgun was an early cartridge-firing repeating shotgun that could carry and fire four rounds without reloading. It was offered in both 12ga and 16ga (this one is 12ga) and used a rather unusual open-bolt mechanism. Cocking the hammer fully would bring a shell into position between the bolt and chamber, and firing the gun would cause the bolt to drop forward, chamber the cartridge, lock in place, and immediately fire. Re-cocking the hammer would extract the fired case but leave it in the rotary magazine, and then bring a new shell into position to be fired. As a result, one could fire four rounds and then would have to unload the 4 empty shells form the magazine carousel before reloading.

Roper would go on to share the patents for the first pump action shotgun with Christopher Spencer (better known for his lever action rifle used in the Civil War) before his ultimate death on a steam-powered velocipede (we all have to die eventually, and that was a cool way to go!).