The motor barrel is an old American system 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. The purpose of this arrangement was that if the spring breaks, destructive recoil forces would not be applied to the gear train.
The Illinois Bunn Special and Hamilton 950 are two great examples of high-grade pocket watches that use a motor barrel in their movements
The system is comprised of many parts compared to a traditional barrel.
Traditional barrel and its parts
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CHARLEY PHOTO OF THE WEEK: Here’s Charley taking a pre-bed nap after a long day of being a good girl. Her weekend plans include getting a bone, taking naps and watching 60 Minutes.