Their products do seem interesting if you are into this kind of stuff.
http://www.knoxx.com/product/COPstock.html
http://www.knoxx.com/product/COPstock.html
I am sending out a replacement stock today. I apologize for the problem. Please discard the old stock so that it cannot be reused. We have researched the reason for the problem and found that a very few units were assembled with the wrong pin in the receiver extension. This can allow the overtravel
you have experienced. We have gone through our entire inventory and replaced all of the pins in the units so affected. Please let me know when you receive the new one.