The Motor Barrel is an old American system that was used in the highest grade Railroad watches, like the Illinois Bunn Special and the Hamilton 950. The Motor Barrel allows the mainspring barrel to ride between jewels when the watch is running. In America's great watchmaking past, there were two Motor Barrel types: one protected the movement if the mainspring broke; a later system reduced wear and friction, and made a more stable barrel in the movement. We use the later system. Prior to the Caliber 20, the last watch with a Motor Barrel was made more than 50 years ago.
The system is comprised of many parts compared to a traditional barrel as you can see in our exploded view drawing. You can see a similar system in the Elgin cutaway drawing.