I had a M-223 4x16x42 (M-Tactical) for about 5 years, on a 16" AR upper. Actually it worked pretty well and I never had any issues with it, but, I d/n like the 600 BDC ret., because it never aligned with any of the factory ammo that I used, so, it was a waste. Glass was clear enough and I could hit with it, so, it was doable for awhile, but, then I moved on. I'd spend money on something else, since they're out of the rifle scope business now. Mac