Is it legal to make and fire your own projectiles from BallMaker molds?
Making projectiles (non-explosive) is not illegal, the materials they are made of are allowed and such ammo can be done as a hobby.
Shooting such projectiles depends on the individual law in which country you are. Usually, the law regulates what the highest energy may be while projectiles exit the barrel. Usually it is 7-17 J, so that the weight of the projectiles should be controlled. Their power should not exceed the power allowed in a given Region.
Shooting long nails or spikes can be controversial and deadly. There is the risk of causing damage to the health or life of other people. Shooting by these in public places may result in a fine, a court and prison.
Remember that you shoot self-cast projectiles at your own risk!
Remember that damaged weapons caused by firing these projectiles are not subject to complaint!
Don't shoot people and animals!