On a properly made box lock the third bite will lock up the action when fully closed, that is part of the hand fitting when filling up the action. Therefore it will assist in holding the barrels to the face upon firing and is not a safety lug like on a Mauser which does not contact anything during normal operation until there is an overload.
Only poor quality guns have clearance between the pin and the hole on the third bite.

Waidmannsheil.