Infantry828,
The mount on the barrel is necessary to allow correct eye relief while mounting the scope as low as practical and not having the objective bell strike the rifle when tipping the scope up to mount or dismount it. Otherwise, to have the front mount on the receiver (with correct eye relief) would either require extremely high mounts or "Contra Einhackmontage ", where the front mount locks the scope which tips up in the front and requires bolt removal to prevent the scope striking it when mounting or dismounting it (these mounts were made by ERA but I believe no longer).
Mike
