The vapor trail thing is what snipers use to track and spot where the bullet hit, it's actually a disruption of the air that can be seen from a position behind or to the side of the shooter.
50 BMG will go through armor plate and mechanicals that an ought six won't. I've put one through the engine of a car lying on it's side.
Based on a scaled up .30-06 has zero relationship to power comparisons with one.
Fiction is harder to write than the truth, fiction has to make sense, the truth can be unbelievable.