Several variants of the mitrailleuse concept were developed, with common elements to all of their designs. They were characterized by a number of rifled barrels clustered together and mounted on a conventional artillery chassis or (in the case of one model) a tripod. The ammunition was secured in a single block and placed into the breech, behind the open ends of the barrels. All of the barrels were loaded simultaneously by a manual closing lever or large horizontal screw. A second lever could be worked rapidly (or in some models, a crank could be turned) to fire each barrel in succession. This earned the weapon its French nickname of "moulin à café" (coffee grinder). (A very similar name was earned by the hand-cranked, mechanically loaded, continuous-firing, "coffee mill gun" in America during the American Civil War.)