I recently got a 300 RUM and have started load development on it. I am using 200 Barnes LRX and Retumbo with Federal 215's I first planned on starting around 90 Gr. but after consulting my Barnes manual they had a much lower starting charge... in the 70's which I found to be ridiculous.. even their max charge seemed low but reluctantly I started within their parameters and have now worked from 87 grains up to 92. I wasnt seeing much velocity increase till I got to about 89 grains, before that it was stuck at about 2950ish. and grouping seemed sub par. at 90.5 I started hitting the low 3100's and it has kind of plateaued but my groups are shrinking dramatically. I am monitoring pressure signs, the bolt lift is getting slightly stiffer but not bad I expect to find max pressure within a grain or so Then I will try it out for a while reloading the same few pieces of brass over and over to see what kind of life I can expect out of my brass. I may have to adjust it if it wears brass out too fast. I have a new box of Nosler brass sitting here and I hear its softer than other brass so I want to be sure I dont wear it out right away. I will keep you guys posted and maybe be able to come up with some useful load data for someone wanting to use 200 LRX with retumbo.