Mortar Round?

[GOOSEONE]

I have a 12lb brass coehorn mortar which I have just begun to shoot. I noticed in a few pictures of mortar rounds used by competitve shooters, many of the balls have a nail/spike sticking out of the round balls. Can anyone help me understand what purpose these nails serve? Unless there is something obvious I am missing, I just can't wrap my head around the idea.
Thanks for any feedback given

[John Holland]

Nothing should be protruding above the surface of the ball itself. If you see evidence if an iron rod on both sides of the ball, and flush with the surface, it will be a ball cast around a core. The core is suspended in the center of the mould on a rod when the molten metal is poured into the mould.

[Dheisey#7003]

John has the right of it. The sand core is supported in the mould with the steel rods to keep it in the center of the projectile. There are projectile moulds that do not use rods to center the core, but they are expensive to have made and are difficult to use.