[marktwain]

It’s far more than you could fire a bullet.

It is 7,800 fps.

Some specialized cannon (Gerald Bull’s super gun designs, and some gas guns) have already exceeded that number.

Rail guns do so regularily.

Firing projectiles form the moon to cause nuclear level impacts on the earth is completely doable.

It requires a significant technological presence on the moon.

Could an asteroid belt based system do it easier? Maybe.

[Telepathic Intruder]

I get 3,096 fps (v²=2Gm/r). In any case, yes only a high-tech gun could fire something at that speed, but then it would be small enough to just burn up in earth's atmosphere if given that (very precise) trajectory. The meteor that hit over Russia recently was several meters across. Launching something like that from the moon would be a major undertaking.