Quacker-Wacker

Are there any optional shims available for a SBE II other than the 4 that come with the gun.(Z,A,B and C.) I need a D shim.

Got my new SBE II and love it. I got it shimed so it fits me perfect (C shim). My problem is that the center of the pattern is about 6" above than the point of aim. This is when shooting patterns off of sand bags. Is there any way to bring my pattern down. I heard somewere that there is an adjustment with the barrel stop on the magazine tube. Is this true? If so, how do I do it. Any info would be greatly appreciated.