A cool paper weight indeed!
Looked closer at the Navy site forwarded (Thanks for that) and did not see what the model "10 MMP" was as far as type of projectile? Would also assume this was a WWII shell?
How the heck does a 10 year old kid in MN end-up with something like this forty years ago? When I was in the Army there would have been no way to get your hands on something like this.