It is a brass case with a Berdan primer with 2 flash holes (copper primer cup). This case has no headstamp of any kind. It has a very old looking domed head. It appears to have been pulled and looks to have containted blackpowder propellant as the primer is unsnapped and it has blackpowder type corrosion on the inner case walls. The case also has a hole dorroded in it, and the case may have swelled where the blackpowder absorbed moisture.
Calibre: About .42" (11mm) (I can’t say for certain as the neck is mis-shapen).
Case length: 1.12" (28.5mm)
Case dia. at mouth: Neck to damaged to give meaningful measurement, wall thickness obout 0.012" (0.3mm)
Rim thickness: 0.4" (1mm)
Case outside dia.: above rim: 0.479" 11.9mm
Rim dia.: .530" (13.46mm)
Cartridge case from side: (9mm Para round for scale):
Does anyone have any idea what this is? I would be grateful if you could identify it.