I have done several searches and have found things similar but not like this. It is about 14 inches tall. I believe it is some kind of mortar shell.
That looks to the the sub-projectile from a US 105mm M724A1 TPDS projectile that has been attached to a home-made body.
More photos and info can be found on this old IAA thread: Sectioned 105MM TPDS M737 Projectile
I fully agree with Spaceinvader, something “very self made”.