OK folks, the muzzle velocity of a 7.62mm AK47 round is 2300 feet per second...(710m/s)...
Who's got a trajectory program? What goes UP must come down, what's the speed and energy at impact?
Assuming it goes straight up, it will come down with the muzzle velocity minus some effect of air resistance. It would very likely reach terminal velocity...more than adequate to kill, punch holes in roofs, cars etc.
V = (2mg/CpA)^1/2
mass ~ 20 g
A = 4.56x10^-5 m^2
Terminal velocity = 40.79 m/s Approx 91 mph