I don't use H1000 or Retumbo in the 300 Norma but I have found it to be very easy to tune cartridge. In one of my rifles I use Norma 217 with 230 grain A-tips with 86.9 grains shoots amazing (3063 fps) and I would not recommend for anyone to run this load in another barrel. Because it is impossible to find this powder anymore, I have been experimenting with different powders in another rifle still a work in progress due to time constraints.
For this rifle, also chambered in 300 Norma I am using a 26" CA carbon fiber barrel. I tried 85-87 grains of VV N570 and BMG 50 with 225 gr. ELD-Ms all of which shot very well across the entire range. The velocity with BMG 50 was too low so I need to run more tests at higher charge weights.
I would recommend you try Retumbo with the 230 gr. berger (I think Retumbo will give you better case fill). Any quality brass should work, I recommend you anneal and bump the shoulder 0.002" so as to minimize brass wear. Attaching someone else's information previously presented on this forum:
View attachment 8501332
Hope this helps...