I have no issues with the fixed 3 power. Nikon makes 1-4 variable scopes so check them out. I agree with you about the 3-9x40 for your purpose. I had one on my lightweight AR and it was just too big. I had to keep the adjustable stock fully extended and the weight was noticeable. I like small carbine scopes on M-4 style ARs so I can keep the stock short and the gun light. For a long range setup a full size AR and high power scope would be better suited.