I need to remove the rib off the barrel of my .50 Cal T/C Scout rifle. There were three screws on the rib that were no issue but under the Thimble w/ Swivel Stud there is some type of screw holding it to the barrel. If it is a screw it does not have a slot like the others and there appears to be a round hole on top but it is not a torx or allen screw from what I can tell. Can someone please explain to me how to remove this last screw to get the rib off. Very much would appreciate some help.