In broad embodiment, the present invention is a mechanism that allows one to impede the movement of a firearms adjustable and or collapsible butt stock. The device wraps around the buffer tube or stock shaft of a firearm and prevents to the movement of the previously adjustable portion of the firearm stock. The variable shaft locking device can be easily attached and removed, and allows a user to temporarily “lock” the adjustable portion without damaging the firearm or impeding its functionality.