The smithy gives you a stack of 2 cannon balls after you craft it even though the max stack of cannon balls is one so you need to seperate them by either dropping and picking them up or manually transferring one at a time to an inventory

If you didn't know this and are traveling with 15 stacks of 2 cannonballs and you reload your game... 🥶 you just lost 15 cannonballs as the game will automatically set the 15 stacks of 2 cannonballs into 15 stacks of one cannonball.