This would not explain the plastic part of the object, however.
"Much that once was, is lost. For none now live who remember it."
The pic above is that of a brass case.........
It is metal and does look like bullet. But not sure about it!
Can't help sharing this link to a cute novel site that is different from anything I have seen before. Should be interesting for anyone that like their stuff to be reused or to buy second-hand. :) http://www.jumblets.com
Oh. Ok.....a bit of education......
Bullet - The projectile that leaves the barrel of a gun when fired and travels, at high speed, through the air until it hits something.
Cartridge - The brass case that contains the propellent charge to 'shoot' a bullet from a gun
Round - A cartridge and a bullet that are together as one piece
What you think you had was a bullet. The picture you've shown is a cartridge. These are two totally different things. What you found is a lump of metal that is vaguely bullet shaped, but not a bullet. It is more likely an old battery or something similar.
The cartridge case in question in the above post is a 20mm Hispano, considerably larger than our unknown object which I think we have all agreed is not a bullet.
British Military Smallarms and Ammunition
Collector, Researcher and Pedant
Yes, I've gotten that it's not a bullet, but couldn't delete the word "bullet" from the post - sorry about that.
I thought the other one above looked like it had a plastic end (the one Tony says is a 20 mm Hispano) like our unknown object.
I've begun researching batteries now.... we'll figure it out one of these days Thanks for your help everyone!