Scott, just looking at the way that my revolvers work, the balls are not spherical once they're loaded - and they get even more deformed when they're shot.
That .457" ball goes into a .450" cylinder, then .440" lands. It's not a sphere when it comes out of the muzzle. Oh, it's not elongated like a contemporary bullet, but it's longer than it is wide.
Also, a sphere can behave like a gyroscope. With sufficient angular velocity, the sphere will resist torques along its axis - which tend to keep it moving along a straight path (this is an enormously simplified statement of what's happening, of course).
And, just ruminating here, I'd think that another factor that is required for outside forces to act upon projectile is time. A bullet isn't in the air for all that long before it either strikes a target or the ground.
But I'm no expert on the subject - I work with electricity; I play with bullets!
Well we don't rent pigs and I figure it's better to say it right out front because a man that does like to rent pigs is... he's hard to stop - Gus McCrae