I recently saw a PMII 3-12x50 for sale that had no parallax adjustment and it was stated it was calibrated for shots out to 300yds. So does this mean beyond 300yds that the scope wouldn't perform well? At what distances would the scope absolutely become impaired for use without the parallax feature? I would think that this could be generalized to other scopes without parallax, correct me if I'm wrong. Thanks.