Other powders I've used recently are H4350 w/ 220 gr Sierra, H1000 w/ 220 gr Sierra.
My previous best load on the old barrel was with H4831SC w/ 220gr Sierra projectiles, which is why I started there this time.
The lands on my barrel start at 2.845" (on a bullet seated overlong and died prior to chambering, measured from rear of casing to first rifling markings).
Important to measure this early on, so you have an idea of throat erosion over the life of your barrel. 300 Win Mag isn't a pop-gun, you'll be fortunate to get 1500-2000 shots out of it.
As throat erosion slowly steals you of nice crisp lands, your optimal cartridge OAL length will gradually lengthen, you'll need to keep up with it to retain accuracy.
As my throat erosion went on in the old barrel, I kept my CAOL growing to match, and stumbled on a sweet spot with those 220 gr sierras WAY the hell too long. It confused me for awhile, why a rifle that'd historically shot .75 MOA suddenly was shooting .3 MOA.
Needless to say it was kind of exciting and I shot the heck out of the thing for awhile.
I struggled with finding the answer until one day I just stared at a round I'd just finished loading on the bench. I took an unseated projectile and put it next to a loaded round, comparing where the tip of the bullet was, and found that the boattail of the seated 220 gr bullets were precisely at the neck/shoulder junction on the casing. I mean, exactly.
I figured it's a phenomenon worth re-testing.
My lands are still intact on the new barrel, so I can't load 220 gr's long enough to line them up this way - they'd be jammed .2" in to the dang rifling if I tried.
So I'm going with a lighter bullet, to see if I can match it up better.
