Was it this Gatling gun that fired the “1inch Gatling Inside-primed rimfire”?
(The barrel diameter looks a little big, but I was just curious)
The sign (when blown up) indicates this one is .58 caliber, and is one of the few obtained by ADM Farragut near the end of the Civil War for use by the Mississippi Flotilla. Apparently the U.S. Navy tested some of the early Gatling guns at the Washington Navy Yard in May and July, 1863, and found them to suffer from gas leakage, ammunition feed and rifling problems.
Judging by the exposed rotary sprocket (not the official name, but descriptive to indicate the part to focus on) this is one of the very first types which used the steel chambers which were loaded with powder and Minie ball and percussion cap, not a self contained metallic cartridge. I don’t think I have ever seen a photo of one of these before, only the later cartridge types. Apparently, the U.S. Army converted all their early style Gatlings to use the .58 rimfire cartridges in a modified (bored through) chamber device, and I believe later were extensively modified to use .50-70 cartridges.
It appears that the chamber was simply pressed against the breech end of the barrel, not inserted into it as with later cartridge versions, probably causing the gas leakage. The walls of the chamber were sufficient to withstand the force of firing, and did not depend on being inside a barrel like a cartridge. No extractor was needed, and expended chambers would drop out of the sprocket by gravity. The chambers would then be reloaded by the gun crew or assistants.
Here is a photo of a replica of the steel chamber device for the percussion style .58 Gatling guns, shown with a .30-06 cartridge for scale.
(Note: I am still looking for measurement info on the somewhat similar chamber type adapters used with the 16 GA Roper revolving shotguns.)