Retumbo is a little on the fast side, and while I am getting 3,400 easily with Lapua 123s, I couldn't get decent speeds with the 140s and gave them up for the time being. FWIW, zeroed at 100 yards, I need 19 moa to be back on at 1k with the 123s.
IMR 7828 was WAY too fast for me, and I hit high pressures quickly with any useful bullet weight. I did shoot a couple Sierra 87 grain varmint bullets with it, which blew up in the bore or at the muzzle - guess they're not rated at 4k+ . . . ;-)
Seems like H-1000 would be a little fast for it too, but I haven't tried it.
I am advised AA8700 is VERY close to H-870 in rate, but cleaner.
Were it not for the horrific fouling and then lack of availability, I would still be using H-870. With a 30" barrel, I was able to exceed 3,550 with Nosler 120 BTs with H-870, and got 3,400 with 140s pretty easily using 83.0 grains. Both loads were 1/4 to 3/8 moa loads.
I had tried H-5010, and, while it was rated slower, the lot I had was about equal in burning rate to H-870. At the time, I had a bunch of H-870 and there was no motivation to work up another load with such a close approximation. Now, with H-870 about gone, and a PIA anyway, I would reconsider H-5010, and would hope for less mess.
Before fully understanding my problem(s) with this cartridge vs H-870 vs hard carbon, I had asked for help over at Accurate Reloading. I was offered a great deal of advice, both on substitute powders and on dealing with the excessive fouling. You might find that thread interesting:
Replacing H-870 in a 6.5-300Wby ?? - Topic Powered by eve community
My info/experience with this rifle has stagnated since then. At 750 rounds, I had it set back and re-crowned. Had to go 2" up the bore to get a decent indicator reading and the throat was SO ugly to that point, I decided to just grab the first *decent* load and quit making it sore just playing with it. With about 74 grains of Retumbo and the 123s, I got good velocity and excellent accuracy and have tried to slow down the round count a little by focusing mainly on hunting with it.