Re: Rock River PDS
I replaced the stock with the RRA Operator when I bought mine. It's a big improvement (its no UBR, though)over the tupperware that comes with the PDS.
Sighting with an eotech and 3x magnifier, I was consistently hitting a 2.5" spinner at 100 yds. I've since bought an Aimpoint T1 for it, but haven't had a chance to mount it.
I got the version with the ribbed hand guard, and I couldn't be happier with it. It provides an ergonomic grip that looks, and feels, better than a quad rail.