WWII 40MM Dummy Cartridge

It belonged to the Navy it's marked with the Anchor symbol. Some other markings are 40MM Dummy Cartridge, MK1 & MK3, 3, 1943, Lot 2103. My Grandpa was a Marine in WWII he told me stories about running off the boat onto the beach trying to not get shot. I just love this piece. If anyone has anymore information about this item or knows where I could go to find out the specifics of the lot numbers and stamped info on it I would greatly appreciate it.