.The Flobert cartridge was developed by the inventor of breech action firearm, Mr Flobert of Belgium  in the
mid 1800's. It was known as "
The Garden Shotgun" and made by many manufacturers in the early to mid 1900's for
short-range shooting  of small rodents.
Winchester introduced their version, the "Winchester Model 36 Shotgun" in 1920 and only made 20,306 guns; the
firearm was discontinued in 1927 and Winchester stopped production of the cartridge some time shortly after 1927.
Again, there are many different 9mm rim-fire shotguns in the U.S. and all  should be able to use these cartridges,
but as with any firearm it is up to the owner to make sure the firearm is in
good working order before using it.
These cartridges are 1.439" or 36.56mm long, the rim is .406" or 10.33mm in diameter, the case base diameter above
the  rim is .342" or 8.7mm in diameter, and the top of the case is .326" or 8.3mm in diameter.
Works in Winchester Model 36 Shotgun and most all 9mm Garden shotguns
9mm Rimfire Shot Shell
The smaller the shot number, the larger the shot - 8 shot
is smaller than 7
&1/2, and 7&1/2 is smaller than 6 shot, etc...