the moon example has me confused, you fire a bullet straight up even with out atmosphere it would still slow down down and then start to fall back to the surface, starting from a certain altitude, it would then accelerate uniformly until it hit the surface, so your constant velocity thing either doesn’t add up or I missed something.

In fact, firing a bullet straight up on the moon, with no atmosphere and 1/6 gravity, it may have escape velocity and never come back,

Guns are a riddle, we’d all like to see a world without them, but, no one trusts the government to take them all away.