Will not fit properly - FAB Defense Heckler & Koch MP5 Aluminum Scope Mount

I have tried this on Zenith and POF MP5 pistol, and both times it will not fit either of the weapons without some rework of the rail mount. At this time I have not tried to rework where it sit onto the saddle of the weapon. I have email the manufacture on several occasion with no reply to solve this problem. There various ways I can solve this problem with a little filing of the sides of the rail to fit over the rear of the weapon where the weapon hits the sides of the rail mount. Stand by for further detail.