If you look directly at the back of the rifles stock you will see a roundish plastic cover. It protects an opening inside of the stock for storage. (This is the piece I am missing)
Directly below that is a flathead screw which secures the butt to the stock.
Sorry there is no photo, but I cannot seem to add one?
I just purchased a Smith & Wesson M&P15 Sport II and after coming home from the range I found the small cap on the rear of the stock gone. I called the range figuring it fell off while shooting. NO LUCK!
I have looked every where to find the part but with no luck. If anyone knows where I can find one or even the correct name for the missing piece or part number, I would really appreciate your help!!