Cannonballs are spherically shaped projectiles generally made of solid iron and are fired using cannons. Historically they were fired using a mounted cannon packed with gunpowder and ignited with a burning fuse.
Can be found by the eyebot pod in various containers in the Commonwealth.
Two can be found in a bucket in the Nucleus, up in the catwalks at the end of the first hallway to the west after exiting the end of the Nucleus Command Center, next to a huge pile of cans.
Five can be found among the wreckage of the Bar Harbor Museum, along the shore east-northeast of the Cliff's Edge Hotel. Three in a peach basket inside the building wreckage and two more in the adjacent crevice next to the cannon.
Eight can be found next to a submerged cannon directly west of the southernmost pier of the Fringe Cove docks and directly north of the large sunken ship.