Little confused about deletemovieClip

1

i am working on a game where bullets fly across the screen from right to left and i have successfully created the movie clip and made it duplicate itself. but i need to figure out how to make the movieclip delete itself once outside the movie frame.


onClipEvent (enterFrame) {
    if (this.hitTest(_root.plane)) {
        _root.planehealth -= 5;
    }
    dupMovie = function () { for (i=0; i<4; i++) {_root.bullet.duplicateMovieClip("bullet"+i, i, { _y:Math.random()*250} );with (eval("bullet"+i)); {_x-=15};}};
    dupMovie();
    if (this._y<0) {
        removeMovieClip(this);
        ;
    }
}

anyone know how to properly delete movie clips?
~MikeG