I have been looking at pictures of trade pistols. Many of them show no visible attachment method for the rear or lower portion of the trigger guard. That is, I cannot see any screws or even pins. The front seems to be pinned in the normal manner. The investment cast iron guard I recently purchased has the appropriate tab on the front for the pin. It has a sprue on the rear where it was cast. Should this sprue be filed and ground into an additional pin tab?