Stanton Percussion Turret Rifle
Probably not more than 60 of these unique guns were ever produced .. somewhere around 1856. The turret had 6 hinged chambers which hung suspended under the gun. When the lever was opened it rotated the turret and cammed a chamber into line with the barrel. Closing the lever slid a gas seal around the front of the chamber.
It was said to be a very "speedy" operating action, and was a different approach, trying to deal with the gas leakage at the cylinder/barrel breech.