Looked at the picture and I don't believe that the notch/cutout is factory. It appears the removal of wood has left an area that is open to the receiver for dirt, dust, grime and other material to enter the gun. The screw holes may be factory for a receiver sight and I believe I have seen receiver sights mentioned for this gun. As to jamming, I suppose that some would say it is a jamamatic, but if you look at the design and the close tolerances, there really isn't much of any place that powder residue, fouling, etc, can escape to, so extra effort must be made to keep clean and lubed. But then aren't we supposed to be doing those things anyway ?