Tell your buddy that he needs to go back to school.

The Earths surface curves about 8 inches per mile. So at 5 miles the earth curves about 40 inches. So unless your buddy has some new over the horrizon capeable bullets with their own built in radar system it is not possible for him to see, much less hit a target five miles away from a sitting or prone position even if the bullet would travel that far.

And that would be one hell of an offhand shot standing up.