Removing movieclips problem

I have my guy who shoots at blocks. I want it so that when the bullets hit the blocks, the bullet dissapears and the block dissapears. right now, im using ._alpha because i couldnt get the removemovieclip() to work.

here is my code on the block:

_root.b1._alpha = 0;
_root.score += 1;

so since im using alpha, i can keep shooting the block and get points, which is a bad thing :stuck_out_tongue: