Ultradyne USA Weighted Bag Rider, Fits UD Adjustable Butt Stock, Nitride Finish, Black, 2 M-LOK Slots, 2 Lbs UD20069 Ultradyne has fine-tuned the design of the Adjustable Butt Stock by offering optional weights for optimal performance in both hunting and competition settings. The Adjustable Butt Stock is already lightweight (just over 1 pound) with the principle that it is easier to add weight than to remove it from the structural design. Weight can be added by attaching one of the weighted Bag Riders. Whether you're building a lightweight hunting rifle or a heavy competition rifle" the bag rider and weight options provide the flexibility to tailor a build to your exact needs.