I dont own any Nightforce scope right now. I also dont own a Accuracy International. But I can tell you its a much better built rifle than any Remington, Ruger, or Savage. Not that they arent good though.
The Difference between the nikon m223 and Nightforce is not just price. With the Nightforce you get:
more reticle choices
30mm tube
mil/mil option
zero stop
much better glass
much better build quality
Nightforces track record for some of the toughest optics ever.
Many people would never notice these diffences but some do and are willing to pay for the better quality scope. Just like I would never buy a high end sports car, but I wont say a mustang is the same thing for less money. Im not knocking the Nikon, but it is what it is.
