Re: what the hell is this?
That is a 40mm TP (training practice)Round, DODIC B584, M918 Linked. It is fired out of a MK-19. The B584 has a spotting charge in the back of the round. Because the back end has been blown out, thats the jagged metal you see at the back. It is a sensitive fuse round because of the spotting charge. We have a hand full of these things in the office. It can't hurt you, it has been fired and functioned. But you should have just left it alone. if you need to know what it is take a picture. Never pick up UXO.