I'm not familiar with the Rock River....is that a semi auto? I've had some trouble with extraction/ejection issues in my Chicom M-14; best I've found (for function in a semiauto) so far has been H4895, and I've heard that IMR 4895 is good as well. I'm shooting 150 grain Remington PSP bullets.. the bulk stuff.
Having said that, as far as accuracy goes, I've done well with IMR 4064 and 150 grain bullets, and H335 and 165 grain bullets. Hope this helps......
....and Welcome to the boards, Matt!
