After having a few problems already which were repaired by warranty service (now out of warranty) I found a loose part inside the gun. I can see the part in the exploded view, but there is no indicator as to which part it is and I'm not sure it's listed on the next page. The screw holding the part from the left side of the receiver must have came loose. I believe I hunted all last weekend with this part not installed but don't trust it.

Anyone have an idea what this part does?

Thanks.