Mounted my Nikon M308 scope with a single piece mount to my new Ar10. The first trip to the range, altitude was near dead nuts on. However, it was shooting far to the left: like 8 inches at 25 yards. Is this usual? should I be reassessing the process of mounting the scope to the picatinny rail? I don't want to take up all available windage adjustment just to get it to zero.