I love my Nikon Buckmasters 6-18x40 SF for the price. Great scope! I use it on my 223 and shoot to 500 yards regularly. I have not had any problems returning to zero. I also use this 223 as my primary coyote hunting rifle and I hike all over in some rough terrain. It's never lost zero.
My only complaint is the thickness of the standard plex recticle. I wish it was thinner, perhaps I should have gone with the target dot model (not all stores carry that model but it IS available).
Here are some pics through the scope at 500 yards from last week. It was 90+ degrees with a little mirage and light wind downrange. The white targets on the left and center are paper plates with a 3" orange dot. The target on the right is a 10" steel gong with the same orange dot. Set on 18x power.
The mirage is distorting the clarity of this image. But it gives you an idea of how thick the standard plex recticle is at 500 yards on 18x power.
Savage 12 FV 223 Remington
Glass bedded action, forend stiffened with bedded iron rod
Nikon Buckmasters 6-18x40 SF TT
Harris 9-13 typeS bipod
Hornady 40gr Vmax
Video of me shooting that 5-shot group at 500:
YouTube - 223 at 500 Yards
(I can't figure out how to embed the video so here's the link)