I wouldn't use a fully decked out entry type AR for any long range varminter. Two completely different firearms designed for two completely different applications. I am sure it would work for fairly short range varmints but I wouldn't even attempt it at 300 yards..... well I probably would but I wouldn't expect to hit anything I was aiming at.

Unless you are building a full blown custom AR for competition then why would anyone want to build (assemble) one? There are variants of the AR out there to suit everyones needs that can be exceptionally accurae with out going through the headache of getting all the right parts together.

If I ever decide to purchase an AR it will most likely be a DPMS Panther super bull.