[Herb]

Aaron, I had the same problem with my Erfurt. I used an inside caliper and found that the forward inside measurements of the cannon rails was 13mm and the rear was 11.5mm, my guess is a previous owner may have dropped it and then stepped on it squeezing the rails together at the rear. I used a wooden wedge inserted at the rear and forced the rear portion of the rails out to 18mm and then let it set overnight. It worked, both measure 13mm now. You might check to see if yours are also squeezed together at the rear.