....so I'll chime in for answer #4:
Rifles must have a barrel length of at least 16" and an overall length of 26".
If you have a folding or collapsable stock, ATF measures OAL with stock extended. (I believe one state measures with stock folded)
Measure 26" (or more) from the muzzle on a line parallel with the bore and mark it on the stock. Cut.
Thats as close as you'll get to the "looks" of a Ruger Charger.