[mre]

var i:int;
var len:int = bullets.length;
var b:bullet;
for (i = 0; i < len; i++)
{
    b = bullets[i] as bullet;
    if (b != null)
    {
        b.x += b.speed;
        b.lifepoints--;
        if (b.lifepoints <= 0) 
        {
            bullets[i] = null;
            if (contains(b)) removeChild(b);
        }
    }
}