I have the Blackfeather on my 2007 M14S. The only other upgrades are the fluted spring guide, shimmed gas system and installed the Casm Mount. Accuracy is around 1 1/2 to 2 inches. Usually closer to 1 1/2 but can't seem to get under that consistently for 5 targets of 5 shot groups!
Still pretty good for a "battle rifle". I have been using the Hornady 168 grain match, am going to try 150 grain and 125 grain bullets when I can find some, seems that the Hornday Amax do as well and sometines better than the match bullets in this rifle and my M1A also.
Rodney