No specifics yet on round involved, I just posting pics in response to your reference to Bofors 40mm remark, hope it helps give some scale to possible round.. I had a couple teachers that had spent 20 and 40mm rounds as doorstops and shelf display.
Yep, if they are spent that is fine, but this guy must have had rocks in his head not to recognize a live round when he sees it:) I had an ashtray(wish I still had it) made out of a 5 inch round(it had no primer and was cut off about 4 inches above the rim) from WWII. It was quite a conversation piece!