I’ve stumbled upon your what appears to be a sophisticated community that really knows a thing or two about ammo, and also upon this odd shell that I was hoping you guys could help me identify.
It looks similar to a 410 gauge, but shorter and has a full brass casing.
I’ve tried searching for possible matches but couldn’t find anything anywhere. Either way, here it is:
I’ve included all possible information I could think of and a comparison image with common rounds.
Weighs about as much as the 7.62 nato.