Re: 338-378 improved project
102 grains of Retumbo or 113 grains of US869 topped off with the 300 grain Berger and lit by Fed 215M gets me to 3000+ fps with a 30" barrel. 114 grains of US869 will push things on up to around 3060-3070. I have also used RL25 but mainly with 250 SMKs.
Both are full power loads in my rifle, I can push it a little harder but pressure signs start showing up, so start a little lower and work up if you use these loads.
The jury is still out for me on the Bergers at that speed. They seem to be shooting pretty well for me but I am still testing at this point.