I have 3 shims in the bag that came with the gun: Z, A, and C. NO D! Do I assume the shim on the gun is B? Do not want to take apart just to find out. I have shot Win. Model 12 for 30+ years. It has drop at heel of 1.875 inches. Benelli advertises Cordoba drop at heel of 2 inches. The booklet supplied is in mm. Thus it seems shim B at 55 mm would actually be 2.17 inches... Is this a correct assumption? If so, I may need to replace shim B with Shim A.