It's funny how many times I've looked here (to check empty chamber) but have only noticed last night after cleaning how this part sticks out into the chamber. What is it and what is its function? The piece is also clearly visible from the right side view (looking at the handgun with the muzzle pointing to one's right). In the top-view pic below, the muzzle is pointed to the left. This is a Glock 21SF Gen3. I can't find a good Glock exploded diagram that explains this part.