I have a S&W Model 422 (.22) that I cannot pull the slide back far enough to strip a shell off the top of the clip, so consequently I cannot lock the slide back. I took the left grip off and can see the mechanism, but I still cannot make anything move enough to lock the slide back or to let it come back far enough to strip a fresh shell off of the magazine. It's perfectly clean, what can I do to make it function?