Re: 300 wby with long throat?
Mostly, I'm here to throw in with Hired Gun.
Many rifles shoot best of the lands, that's a known fact. Because of the Weatherby freebore, that's not only hard to achieve but can be dangerous as stated.
Accuracy is a lot about finding the "sweet spot" as your bullet leaves the barrel and having consistent velocity to hit that sweet spot.
Seat to max COAL as per the books and work up loads from there. I can't begin to express how much time ladder tests take off of this process. Once you've found your load, a 300 WBY can be a tremendous shooter. I've built 2 loads for mine that are half MOA and am in the final stages of a load that looks to be 1/4 MOA or tighter. Yes, I keep changing my mind on which bullet I want to shoot.... but isn't that half the fun?
All it takes is One Good Shot!