Re: ? 6.5 284
The 24" tube is part of the problem. Another part is "load data." In the last 20+ years of reloading, it is rare that I have achieved published data in the main references, Nosler, Sierra, Speer.
In the 6.5, try H1000 and Retumbo to see if you can squeeze out a few more fps. It is not likely to do much, however.
I have a similar dilemma I am about to face. My 6.5x284 has a 24" Bartlein barrel on it. My first powder choice will be H4831SC. I don't care near as much about speed as many do. I want precision/accuracy. The Berger bullet is so frangible, when it hits what I'm aiming at it's going to destroy it anyway. In the competition shooter's realm, H4831SC and H4350 are THE TOP two powders.