On very humid summer days at Camp Smith back in NY, spotters would occasionally see what I can only describe as visual atmospheric distortions following rounds on their ways out to the 300 and 600 yard targets.Check out this video. It was a perfect day to see the bullet in flight so I got out the video camera
My favorite along these lines was a .577 Snider Carbine I owned about fifty years ago. You could set up a target at 150-200 yards, touch the thing off, stretch and scratch a bit, take a whiz if need be, then watch the projectile bloop in like a mortar round.That is a pretty cool video, you never hit the spinner though.
I enjoy shooting those little Colibre .22s from my NAA mini revolver. You can watch the bullet leave the bore and see it all the way to the target.