Not sure if they are M77 actions or not, do not want to dig them out, or research to find out, but I can tell you what they like.
Ruger RSM .458 Lott Hornady DGS 500 grain shoots 1.5"
Ruger Frontier .338 Federal Fusion 200 grain shoots 2.5+" (have not tested it with premium, and this group was in very hot weather)
Ruger Gunsite Scout Rifle .308 168 grain Federal Gold Match <1"
I have never shot the white box stuff, good chance groups will close up with match ammunition. I highly recommend the Federal Gold Match and the price is not too bad IMHO.
My Gunsite Scout has really surprised me with its precision, probably in no small part due to the awesome medium contour barrel. If yours is a new rifle, and you do not get better results with match grade ammo, send it off for repair, Ruger stands behind its products well. If it is used, check the crown for wear/ damage, and if all seems alright visually, send it back to Ruger and they may still fix it for you (call first). Hope this helps in some way.