I worked up a good load for my Ruger 300 WM using Remington brass. This load is 60.5 gr of IMR4064, Rem 9 1/2M primers and Nosler Accubond 180 bullets. It shot consistantly 1" or less 5 shot groups.
I recently bought a bag of Winchester brass and loaded up the same thing and was getting much larger groups - some up to 3"+.
I am going to shoot some more this week with the R-P brass and see it gets back to where it was.