A year or so ago, Cabela's had Nikon Prostaff 4-12x BDC reticle scopes on sale so I bought one, thinking it would make a good long range scope for my .300 Weatherby. It's a good clear scope that has an easy to turn (easier than my Leupolds) variable knob.
After I got it home and read more about the BDC system, crosshairs zeroed at 200 yds, and elevation circles for 300, 400, 500, and 600 yds, I decided not to put it on my .300 Wby. First, out of all of the big game animals that I have shot, only a handful were shot at over 300 yds, and none at over 400 yds. Then I checking the BDC circles on live game animals, and even at 12x, the 600 yd circle completely surrounds an entire deer at that range. That would not make an accurate shot.
I ended up putting that scope on my 7mm Rem mag, but I haven't hunted with it yet. I first want to do a lot of range shooting with it, checking the impact point for each circle at least at lowest, mid, and highest power settings. The longest target berm at our range is 430 yds, so I will not be able to test the 500 and 600 yd circles there.
Knowing what I do now, I think I would like a BDC scope for a .22 rimfire rifle, but I don't see them as a viable long range big game rifle scope.