I am having a hard time breaking down a ruger standard .22. Its not a Mark I. I have the manual, original box and papers. I can open the hinge pin on the back strap and can remove slide. I thought the barrel should free from the the grip I can not seem to free the barrel. Because of not being able to free the barrel, it will not go back together with the slide working . any advice or can someone tell me what i am doing wrong