Penetration isn't the issue with 00 buck shot, but rather the lack of penetration in the right spot. With 15 pellets, the likelihood of getting the vitals with more than one pellet is minumal at 50 yards and further because the pellets will be too spread out at that distance.At 70 yards and beyondona running away target,you were wasting ammo.
With a well patterned gun, 50 yards broadside shot is pushing it, again mostly because of the lack of pellets in the 00 . 4 buck would give a better pattern at that range and most likely be more effective.