Re: 7RUM, best powder for sending noz120bt's out at 4k?
RL25 seems slow to me, for light 120's that don't spend much time in the barrel. And that's damn close a filled case at 96.5gr. I'm thinking too much of the charge burns outside of the barrel. I can imagine what the muzzle blast is like. But at 3950, you are basically there.
I've been using RL19 in the standard rem mag, also with pretty amazing results. But I'm thinking it's going to be too fast burning for up to a 25% increase in charge weight pushing a bullet down the same sized hole, in the RUM barrel.
Have you tried RL22 with 120's?
At this point, RL22 is what I plan on starting out with, @85gr, hoping to reach target velocity by low 90's. That is, unless you have already gone through the motions with 22, and the results weren't as good as with 25.
The 7RUM barrel that I have on order now is 26", as that is the longest that can be had with Shaw, I believe, or I would have ordered 2 of them. But after I burn that one up, I do plan on going 30" on next one.