Similar firearm in movie, ' Adios, Sabata' (1971)

You can find this 1971 western dvd in the stores now.
On the dvd cover, the late actor Yul Brynner is a mercenary cowboy gunslinger, named, Indio Black.
Indio Black is firing a very unique lever action firearm similar to Josh Randall's Mares Leg (Mares Laig).
Ah, there is one big difference to Indio's unique weapon. He is pushing a harmonica-shaped cartridge magazine through the left side of the shortened lever action firearm.

My question is, was this an actual historical firearm, or was it an ingenuous Hollywood invention?

Hollywood is full of ingenuous weapons meant to draw attention to the main character as something unique. Even Chuck Connors in "The Rifleman" employed a modified 1892 Winchester that allowed him to shoot off rounds every 0.75 seconds. It looked like the lever action was one of those round loops instead of the typical oval shape.

Check out the photo of "Adios, Sabata" on imdb and let us know what you think about this odd firearm. Was it feasible?