Can anyone help?

Hello! I recently visited Cornwall (England), whilst there I went to St Michaels Mount Castle. I found these items inside rocks on the beach. I smashed the rocks onto the large stones to find out what was inside. On the pictures I have put the rock fragments next to the items to show they were inside a rock. They are all magnetic, although the bullet shaped item is less magnetic than the other items. There is no hole in either end of the bullet shaped thing,its 3cm wide 8cm length, although some of the rock/sand is still stuck to the bottom but I don’t know how to remove it. Any information will be great! !!