Re: .257 Weatherby Vanguard
We have some similar rifles and they are both fussy to load for, rarely can I beat the accuracy we get with Weatherby factory ammo. Having said that, it can certainly be done but you have to try several bullet/powder/seating depth combinations till one clicks. The standard 100 grain Hornady (factory Weatherby ammo) shoots so fast and so accurately that we usually just hunt with it. The .257 is an incredible killer, have seen my son kill caribou with it like they were hit by lightning.
I would check the bedding and barrel channel clearance, make sure the stock bolts are good and tight, then start playing with reloads till you find one your barrel likes. We gave up, tried Nosler, Swift, Barnes, Sierra, Speer bullets with mediocre luck. Finally found a medium velocity practice load using Hornady Spire points that shoots about 3/4" and we hunt with factories. Don't have drops I can share since we haven't shot the rifles much since the mighty .308 Win. took over my shooting.