The ‘propulsion’ bleeds off just as fast under air resistance. You can’t say air resistance counters the vertical speed and claim the horizontal speed stays lethal. That is only true for very horizontal shots and not ones that can reasonably considered to have been fired ‘into the air’.
The truth is that bullets fired with even a little horizontal component tend to remain spin stabilized even after they start back down. What kills isn’t that they still have horizontal velocity. By the time they hit the ground there isn’t enough in the horizontal vector to kill. What happens is because they remain in a point first orientation their terminal velocity is much higher. Only bullets fired almost PERFECTLY vertical will start tumbling on the way back down.
Yes. Spin stabilized and point first. I had to look up the old Mythbusters program where they did it, but by the time I did, others had posted basically the same thing. I was trying to recall they had explained it on the program, but got it wrong.