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.
My thoughts were the same. But there is one more, G under the crown means it was rifled barrel definetly. This barrel has been not only re-chambered, but overbored to smooth bore either.
