Hi. I have some info, collected from here, about loads with Vihtavuori powders. I have written up at least N120 with xtp 300, and those might be pretty close to ones suitable for 300gr deep curl.
I have made only sub-sonics with tinstar & xtp 300 so far. Vihtavuori is only easy-to-get powder here in Finland.
I'm loading for RAR also and next load will be 275 Barnes with N120.
I can check and copy some if you need those. Public opinion in here seems to be that starting load with N110 is about same than with lilgun. So that's one guideline, at least don't go under that with N120.
My own guess is that with longer bullets, N120 and RAR, case capacity will be limiting factor rather than pressure, but THAT'S JUST A GUESS SO FAR, DON'T COUNT ON THAT.