Initially I filed away 1 to 1.5 mm of the top surface of the rear sight and filed a new 'V' notch. This helped but it was not enough. I felt I had no option but to try and raise the height of the the front sight.
When I opened up the front sight this is what I got. The pin was threaded into the barrel and protected by a guard frame held in place by a circular nut at the tip. Initially I thought I could simply stuff a smal ball of paper into the hole in the barrel, but I discovered that the hole went all the way into the barrel.
As regards putting a washer the problem was that the guard frame has a notch that exactly fitted the diameter of the front sight pin, so I would have to use the sight without the guard unless I could find a suitably sized washer. I found an old Meccano set square nut and used a drill to enlarge the hole. It fit well, but broke as soon as I started tightening the sight over it because the hole was too big for the size of the nut.
Finally I had to resort to a crude hack. I cut out three thin washers from an old piece of tin after drilling suitably sized holes. I placed them one on top of the other and screwed the sight in place as seen in the image below. not pretty but it works. The big advantage for me now is that it works fine with Marshal shot flat heads. This is a big deal to me. Marshal shot flat heads are half the price of Mastershot wadcutters.
