I see several people have replied that those are "mortar rounds." Nope... they are WorldWar2 era rifle-grenades. (The hole in the base below the tailfins fits onto the muzzle of a soldier's rifle.)
Another poster is correct in noting that the ones you found are non-explosive "dummy" ones, used for training purposes.
I dug that same model of "dummy" rifle-grenade in a WorldWar2-era hutsite (along with some 1942 Mercury dimes) while relic-hunting on a defunct US military base ...which must remain nameless. ;-)
Regards,
TheCannonballGuy