Okie- more than a state rule, you may be about to have a major collision with Federal law.
Assuming your charger to be the standard .22 PISTOL, adding a shoulder stock to that will drop you into the National Firearms Act. That pistol has a 10 inch barrel. Adding a shoulder stock makes it a rifle.
Rifles must have a 16 inch bbl, and overall length of 26 inches minimum, otherwise you have just "built" a Short Barreled Rifle (SBR). You CAN do it legally, IF you go thru the paperwork with the BATFE (much like buying a machinegun) get approval from your local police chief, submit prints, passport photos, a $200 tax.
Penalty for failing to touch second base? 10 yrs in a Federal prison, $10,000 fine, and loss of your right to ever own ANY firearm again.
If you already know this, and already have the paperwork in place with the ATF, please excuse the lecture.