Actually,I have milled a number of spheres on a Bridgeport with a rotary table and a boring head.You tilt the mill head and pass the cutter tip through the axis of rotation as you rotate the table.Think,the cutter path of a fly cutter or the boring head is a circle.You can always lay a circle on a sphere.You can make a hemispherical cavity(ball mold) the same way with a square ended end mill.
But,thats a side note.
There is a way of rolling the balls between two discs to reform the sprue,etc into a more true sphere.
Your plan of a flintlock is sound.Cap and ball revolvers,too.
Till the EPA makes lead possession a capital crime.