Any good, i hear only good things and they garentee 1/2 MOA. Its a single rail gas block so what kind of buffer tube do i need to use a magpul PRS stock?
It depends on the barrel and load like any other rifle. I like the 123gr A-MAX factory load, as well as Mark's (Precision Firearms) 123gr Lapua Scenar loads. My little 16" Grendel usually groups somewhere around 1 MOA, but I have had my best results with those loads. .79" 4rds at 100yds with the PF 123gr Lapua Scenar in Lapua brass, and 1.69" 4rds at 200yds with the Hornady 123gr A-MAX factory load. They were 4rd groups, not 5 with an excluded "flyer".
I took my little AA 16" out to 1200yds this past weekend at 4400ft ASL and 81 F, and had POA/POI repeatedly within a small natural target in the terrain, which couldn't have been larger than 3ftx4ft. There was no wind, which makes a big difference of course.
Everyone I know of with a Precision Firearms Grendel has reported superb accuracy, since Mark only uses high-end pipes in his Grendel builds, like Lilja, Bartlein, Les Baer, Hart, etc. When I say superb, I mean 1/2 MOA or better. A bad group would be 3/4" at 100yds.