Just as others have said, make sure the allen set screws are removed. To remove the adjustment knob, be careful not to lose the small ball bearing and spring that allows for measured adjustments of the knob (and you can feel the "click") when the bearing falls into one of the indents. Those bearings go running into places that make them hard to find so don't do this on carpet or they're gone! I bought a box of bearings on Amazon for like $8, when MPA charges $8 for one bearing and a spring. Anyways, you should be able to remove the butt plate once everything has been removed. To reinstall the knob and bearing/spring, put the knob back in place and then insert the bearing and then the spring (in that order) from the back side (after removing the allen screw that keeps them in place). Good luck.