I just bought a Ken Farrel Picatinny rail for my short action flat back, because the Nightforce rail that I bought is for round back. The Farrel rail doesn't fit, either. The spacing of the holes from front to back is a little bit different. All these tiny variations are enough to drive someone nuts. Now I need to look again for a rail. Hopefully the third time will be the charm. I may ask if Farrel can just make one with different hole spacing.