30fps isn't much. Terminal velocity for something that size is probably higher than that, but not by a lot. So the risk isn't huge, but it IS there.

The only reason I might not fire into the ground is I don't know what is under the very top. Having the bullet bounce off a rock and come up through my foot or some other part of me just doesn't thrill me.

And firing into the air is an amazingly effective way of getting the attention of search aircraft. Not recommended, but it should work. *laughs*