Thanks to everyone for all the replies. It looks like the top candidates are IMR7828, RL22, RL25, Retumbo, and H1000. 7828 and RL22 got the most responses, so I'll probably try those first and see where I end up. I've always wanted to try H1000 in some of my other cartridges/rifles, so I might give that a look see as well.
Test
