Where did you end up? I’m working on 300 win mag with 205s as well. Using Peterson brass, 24” barrel, 1:9 twist, GM215M, and currently testing N570 and H1000. With the N570 I got to 81.5 grains at 3004 with no signs of pressure. Berger said max load with N570 would be 83.1, which I will need...
I’m working on load development as well for 300 win mag Berger 205. I called Berger and the attached picture is the information I got for the powder I asked for.