A typical 7.62 NATO projectile will drop sub-sonic at around 800 - 900 M after a time of flight of about 1.8 secs (say about 2700 ft after leaving the barrel) - this is affected very little by angle of firing.
At that velocity and range it is STILL imbued with more than 400 ft/lbs of energy and is a very dangerous item to have land in your lap.
It is quite capable of punching right through a refrigerator.
I would, arbitrarily, say that it would need to drop below 500 ft/sec before I would consider it to be
relatively harmless to either human or aircraft skin.
Unfortunately, when fired vertically, it will still be traveling at more than 600 ft/sec at an altitude of 6000 ft.
And the maximum altitude reached is going to be somewhere in the vicinity of 9000 ft before it begins falling to earth.
Which pretty much fits in with ....
.....when I was in basic training in the German army, we learned the safety distance for a G3 (7.52x51) was 3000m
When leaving the barrel it would have been rotating at a rate approaching 200,000 RPM.
That is faster than most small vehicular turbochargers and not that far behind a dentists drill.
The ability to maintain stabilised flight is largely dependent on the ballistic characteristics of the projectile and the rifling pitch of the rifle from which it was dispatched.
If in doubt, please refer to standard ballistics calculators from any of the ammunition / projectile manufacturers.
I used Hornady, because they accommodate vertical firing, either up or down