Hello and welcome to the forum!
I mostly used IMR 7977 in my 257wby but also tested H1000 and a couple others. There was no 7977 data when I started so I researched and found it was usually within a grain of H1000 so i started low and worked up. A great powder with 100-120grain bullets. I ran a 24" tube and my loads were 3570 with a 100 gr Etip, and 3320 with a 117 Hornady interlock. I also worked up loads for 115 partitions and a few others that shot great as well.
The Interlock just folded deer! Great cartridge!