Another change was made that is almost as important as the support rib. I moved the rear take down pin from the right side to the left side of the lower. On older designs the right side had a large counter bore cut to allow the head of the pin to seat. By moving this to the left side the right side becomes much stronger. The left side was not effected because the support rib added enough strength. This change along with the support rib are still in use today.