I can’t recall if our late Bill Wise had any such contraptions. Perhaps it is a modification for a handicapped shooter. If so I hope it worked well for him. If I had to do it I’d use a large rare earth magnet to hold things. No holes required and using a second one should repel the first one to break its hold. I used one that generated 50+ pounds of holding. Impressive and darn near impossible to remove by pulling or even pushing it sideways.