As I said a few posts ago, "high angle" meant "higher than is normal for direct fire". Apologies if I was unclear.
Mythbusters did testing on actual high angle gunfire, though, and concluded that if the round was being fired at a steep enough angle to actually have gravity be able to significantly bleed off the force, then yes, the bullet would be more or less non-lethal when it finally came back down. This happened mostly at very high to vertical angles - the bullet would lose momentum and slow down, stop, and gravity would pull it back down. Really, it would be no different than someone up at the apex of the bullet's flight just dropping a bullet. At worst maybe you'd get a bruise if it hit you.
However, at lower angles where the bullet can mostly maintain it's forward velocity throughout it's arc, the round was probably still very much lethal if it actually hit someone. There's been actually quite few incidents of accidental shootings this way - one medical center in LA reported in a ten year span in the 80s to the 90s over a hundred cases of folks getting hit by bullets fired into the air around the holidays. About a third were killed in the accidents.
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I don't know how true it is, but my high school physics teacher said that a bullet fired into the air would come down with almost exactly the same force it had when it left the barrel, because air resistance on it is negligible and gravity would act equally to slow it down and then to speed it back up, over the same distance. So the force shouldn't really be an issue.
It's not true. The amount of force exerted by the powder charge of a bullet being fired is MUCH greater than anything gravity can impart to the same bullet. The only reason gravity can stop a vertically fired bullet is because gravity exerts a continuous downwards force, whereas the bullet's upward energy is supplied all at once from the powder charge.
Also, the story I related, if it is indeed true, had the soldier using multiple rounds, adjusting his angle as his spotter told him how far he was off target. Which is what "walking fire' means.
-k