I would recommend taking a look at the LW series from Spikes Tactical. For your money, you will get a better bolt carrier group than anything from RR or DPMS, a Lothar Walther 16" stainless steel barrel in 1:8 twist, which is probably the perfect twist for anyone considering a hunting type AR, and a Wylde chamber and a midlength gas system. That's tough to beat spec wise, and it comes in at $725 direct from Spikes, which means you can probably find it for a little less if you shop around. This would give you plenty of leftover cash to get a Rock River lower and trigger group. You would then have the best features of a RR (the trigger), with a much higher quality upper. You can shoot varmints accurately all day long and still feel confident in the durability of your upper. Oh yeah, the Spike's upper will have a lifetime warranty too. To me, this represents just about the perfect medium range plinker/varmint combo out there.
