Using distance instead of hit test...
Code:
function doUpDate() {
        if (Key.isDown(Key.LEFT)) {
                hero._x -= hero.power;
        } else if (Key.isDown(Key.RIGHT)) {
                hero._x += hero.power;
        } else if (Key.isDown(Key.UP)) {
                hero._y -= hero.power;
        } else if (Key.isDown(Key.DOWN)) {
                hero._y += hero.power;
        }
        for (var i in bombs) {
                mc = bombs[i];
                if (mc._currentframe == mc._totalframes) {
                        mc = bombs.splice(i, 1);
                        removeMovieClip(mc);
                        break;
                } else if (mc._currentframe >= 14 && mc.damage == false) {
                        if (getMDistance(hero, mc)< 60) {
                                mc.damage = true;
                                trace("hit");
                        }
                }
        }
}
function getMDistance(p1, p2):Number {
        return Math.abs(p1._x - p2._x) + Math.abs(p1._y - p2._y);
}