If every projectile ever fired from every firearm were laid end to end; every rifle, musket, cannon, missile, grenade, blunderbuss, machinegun, anti-aircraft gun, toy gun - every single projectile that ever left a barrel

If every projectile ever fired from every firearm were laid end to end we'd have one hell of a math problem to solve. Not to mention the effort in finding all of those projectiles. Think of the cost, really - shipping those projectiles. And we'd need to rob a museum or two.