I decided to remove the firing pin from my 45 Shield to clean it. I have reviewed instructions to remove it and I can't get the back plate off of the slide. I have depressed the white plastic where I can see it move away from the back plate but the plate will not budge. Is the 45 Shield any different than the 9 or 40 when it comes to this procedure? It just feels like something else is holding the back plane onto the slide. Any thoughts?