Why are there not more and my nomenclature may be wrong,butt hooks on sporting rifles? The hook on the bottom of my biathlon rifle lets it cantilever into my armpit as i balance the forestock in my left hand. An example of one extending from the top like an M-60 butt would help in the prone.I can imagine one that might pivot,but a simple one on the bottom would seem to really help standing shots. thanks for any input and advice or links.