I remember at my grandparent’s house they had some sort of mortar round (? that's what my cousin called it) that they used to prop open one of those old double-hung windows with a broken sash cord.
It looked like an overgrown .22 round. Probably 2 or 2.5 inches in diameter and maybe 10 – 12 inches long.
It seriously looked like a giant .22 round except it wasn’t a rimfire and the primer had been dimpled. Plus someone had drilled a small hole in the base so you could tell it didn’t have any powder in it.
I always guessed that someone had reloaded it with a giant new bullet after it had been fired because I can’t really imagine anyone drilling a hole in the side to take the powder out… plus the primer had been struck with something.
Heck, that had to be way back in the early 60’s…
Working as a divemaster years ago early 90's), we hobbled onto an undiscovered wreck of a coast gaurd cutter lost during a hurricane in 1943. On it we found racks port and starboard full of still pinned depth charges and cases upon cases of 3" shells from it's deck gun.
Although we left the depth charges well enough alone we did bring back several of the 3" shells and had a munitions expert take them apart to find the primers still working and the cordite still dry and flashed as it should have.
50 years later and 110' under the Atlantic and they still would have worked.