A guy posted this on another website. I can’t answer, but perhaps one of you guys can?
This appears to be a US 90mm AA gun nose fuzed shell. The cap in the nose is the base of a fuze. The forward part is missing.
The set screw in the side has to be released to remove that part and that is likely why it is still in place. These freeze up after time.
Basic EOD rule #1
If you can not see into it , it is LIVE.
I would assume that this is a LIVE high explosive shell and treat it so. Contact the local bomb squad through the Police , Fire Dept. or EOD unit on the nearest military base.
Do not abuse or attempt to inert the projectile. These were designed to kill and they do.
If it is still live having it in hand is a FEDERAL FELONY and in many locations is a state FELONY as well.
Many folks end up throwing these things in lakes and rivers to avoid the problems. This is not a good idea.
In MANY cases the EOD unit or BOMB squad will just blow the thing up.
It is not wise to take chances with shells of this nature.
Agree on the advice: no holes to look into = Treat as a live round. But it is also a piece of memorabilia, it has the line stamped into it NO. 500,000…
Could be a milestone display cartridge but don’t bet your life and fortune on it.
Some years back a serious heavy hitter in the ordnance game from California sold an artillery shell all painted up nice as INERT. It wasn’t. It blew up killing a young person and the resulting suits cost him his business and family. He was a Marine EOD man as was his son.
Also , during WW2 a German chrome plated “inert” S mine on display at the Washington Navy Yard EOD unit exploded and killed.
Imprint on your heart " if you can not see into it, it is LIVE ".