Thank you, That gets the wheels turning, add a piece of thin cutting board slotted for one or two Velcro straps, and no dealing with "tools" mentioned in the reviews
"tools" might make it more stable.
Here's my DIY attempt at a bag rider.
Aluminum box, filled with lead, strip of steel inside forearm and two machine screws to attach.
My F-Open AR needed some weight. About 3 pounds in the bag rider.