What will happen if a bullet were fired from the Moon aiming at Earth?

The .220 Swift remains the fastest commercial cartridge in the world, with a published velocity of 4,665 ft/s (1,422 m/s) and the escape velocity of the MOON is 2,400 m/s so the bullet will not leave the vicinity of the Moon and will eventually return to the surface.

The only ballistic (Non missile) round that would leave the moon would be one coming from a railgun which can reach a velocity of upwards 5–6000 m/s (21,600 km hr).

A railgun Round .

If aimed very accurately which would be very difficult to do it could enter the earth’s atmosphere at a speed in excess of 40,000 km/h or 11,100 m/s .

As the projectile reenters the Earth’s atmosphere it will compress the air ahead of it to a temperature of 8000–10,000ºC and melt and burn up , not striking the ground but vaporizing 15 -20 kilometers above ground maybe terminating in a loud explosion.