I have Nikon P-223 BDC 600 Riflescope
and I love it . I bought this to put on my Stag Model 6 AR with a 24" bull barrel. I wanted a scope that would allow me to shoot out to 600yrds or so. The glass is outstanding for the price. Zeroing the scope was easy, and the adjustments seem to track accurately, and easily return to their previous setting. I haven't gotten it out beyond 150 yards, but have shot many times and it's always been on zero.
I was having trouble deciding between the Rapid Action Turret that allows you to just turn the top turret to your yardage (rather than clicks, or mil's, you set it on 200yrds,300yrds, etc), and aim with crosshairs right on the target, or the BDC reticle with the dots to show your holdover for a given range. With the M223 you have to choose. I discovered the P223 has both systems in one scope. You can use the BDC if you want to holdover, such as if you are competing and need to shoot from 100 to 600 yrds rapidly and don't want to fiddle with the scopes turrets. Or you can use the turret if you prefer, and you will be able to use the crosshairs as normal with no holdover. Granted, the M223 has higher quality glass, but for my needs the cheaper price, acceptable glass, and both systems built into one convinced me to buy this scope.