I remember bullet drop from shooting in rifle matches when I was in the military. At the 600 yard line (slow fire prone) we would turn our spotting scope just a little out of focus and we could see the vapor trail of the bullet as it traveled to the target.
Shooting 173 grain match 30-06 the bullet arc would be as much as 8 feet over the top of the target frame! That vapor trail also let you see the impact of the wind very dramatically too. In a heavy wind the bullet could start out pointed 2-3 targets down the line and then drift and drop right onto the the target that you were shooting at.
This is an interesting observation,. If you want to try, put your scope in line with the bullet path, probably behind the shooter, and turn it a little out of focus.
Roudy