It's not just the Comfortech stocks, you can find stories of guys breaking just about any kind of stock there is on a Lead Sled. If you put on so much weight that the rest doesn't move at all there's a good chance you may run into a problem. Shoot with no weight or maybe up to 20lbs or so and you will probably be fine. The goal should just be to take the edge off, but some people want to make a 7mm Rem Mag feel like a .22 and that energy is going to go somewhere.