Re: 300 RUM....180 Grain Hornady SST
I have limited experience reloading with the 300 RUM, but my first two choices in powder were Retumbo and H1000. My first bullet choices were 180 E-Tips, 200 AB's and 210 Bergers. I went with 97.5 gr of Retumbo pushing 180 E-Tips @ 3400 and sub .5 MOA performance out of a Sendero.
For 180 bullets and Retumbo, I would recomend starting with 92 gr and H1000 I would recomend starting with 90 gr.