Here is what I think may be a 9.4 Dutch Revolver blank. It appears to be loaded with a wood composite wad of some type. I’m not sure if a portion of it has broken off or a top cover wad is missing or if that’s how it was originally loaded.
Rim: 12.42 mm
Base: 10.86 mm
neck: 10.61 mm
Lgt: 20.69 mm
Any thoughts on what it actually is?