If you’ve studied elementary physics, you “know” that a bullet fired straight up comes straight down — and it comes down as fast as it went up. In a vacuum. On earth, air resistance has quite an effect. From What happens when a bullet is fired straight up?:
Hatcher describes one experiment with the 150gr M2 Ball bullet fired vertically. When it came back from vertical (round trip time was about 42.9 seconds) it left only a 1/16 inch dent in a soft pine board that it happened to hit. (Not exactly what it would do at 2700f/s, eh?) Based upon this and similar tests Hatcher concluded that the impact velocity was about 300 f/s, which from additional testing appears to be the terminal velocity (the maximum free fall velocity which is limited by air drag on the body in question) of that bullet falling from any height in the atmosphere. (If I remember correctly from my limited parachuting experience the terminal velocity of a falling person is somewhere around 130 mph or about 200 f/s.)What does not substantially change, even at extreme range, is the rotational speed of the bullet that was imparted by the rifling (around 300k rpm) since the effect of air drag on the rotational velocity in negligible. Thus the gyroscopic action, once the projectile is stabilized, tends to keep the bullet oriented in the same direction, thus the base first (well ok, original position trailing end) return. It is interesting that this was not commonly known until just before WWII. The British had lots of dud antiaircraft rounds that all came back base down, or more correctly oriented to the same elevation as shot from the gun. BTW, this is what raises hob with traditional long range small arms ballistics. With lots of elevation on the bore (past 2,000 or so yards) at the far end many bullet are actually falling sideways and all frontal air drag algorithms are out the window.