Raimey was right insofar as most of these garden guns were built for the 9mm Flobert rimfire. apparently this gun has been rechambered to 9.1x40R and converted from rim- to centerfire. Why? Please consider the proof date, September 1918. WW1 was still going on and civilian ammunition like the 9mm Flobert was largely unavailable. In this situation someone having some reloadable brass, a supply of primers and black powder was at a real advantage. My guess: Someone ordered this gun from one of the small Zella_Mehlis makers, who still had prewar parts in stock, but had it converted to centerfire and rechambered. As a boy, about 1908, my grandfather had a single barrel in 9.1x40R. The gun was either destroyed or liberated in 1945, but I still have the thong-type Berdan decapper and a brass bullet seater. He told me he reloaded his shot cartridges with crumbled newspaper for wadding, a pinch of blackpowder and some shot. He used it to shoot crows, magpies and other small pests around the premises.