ffs, invite the police to have a look at it, it sounds like it could be the business end of on artillary shell, the part that holds the propellant, let me explain, when an artillary round is fired from a gun, there is a small expolsion which sets of the propellant, this propellant rapidly expands and seperates the shell (the object I think you may have) from the warhead (the bit that flies out of the gun towards the enemy). It is extremly dangerous and if it still holds the propellant needs to be gotten rid of
Can I ask where you got it from? your grandad wasn't an Artilliaryman during WW2 was he>