Before you get too involved in mechanical reasons the gun is hard to open, clean the chambers really well. Use some scotch brite on the end of your cleaning tool along with some solvent/oil and really scour it clean. I have cured two doubles of really stiff opening problems with nothing more. If the chambers are not clean it is possible for them to retain the hulls requiring quite a bit of leverage to get the gun open. Also cured a couple of semi autos which wouldn't properly function the same way.
