Just bought a used AL391 Urika 2 and have a question about the plastic adjuster stock shims. The original owner put a plastic shim in for cast off (right ) and put that shim on top of the flat plastic shim I assume came from the factory. Was this correct or should the original flat shim been removed. As is with both plastic shims the gun fits me perfect and shots right where I want it. Will leaving the original shim in cause problems with the stock ? Thanks for your help.