I have a Vortex Diamond Back HP 4-16x on my DPMS .308LR. It is a very nice quality scope and, IMO, is better quality than the Leupold Vari X I line.
Don't get me wrong, the majority of the scopes that I own are Leupold but, when I found the Vortex on sale at the grand opening of a Calbela's for $249.95, I didn't hesitate.

I had been looking for a scope to replace the Burris 1.75 x 5 scope that was on that rifle to take advantage of the accuracy exhibited by the DPMS. I has not let me down in two years of solid use.