Reloader25 for accuracy, Retumbo for highest velocities.
You can reload it on the cheap by using some of the milsurp powders sold by Jeff Bartlett. His web site is:
www.gi-brass.com
I've used WC860 in .257wby., .300RUM, .300winmag, .270wby, and 7mmRemMag.
Works great, but there are significant differences between individual lot#'s.
Also, watch MidwayUSA and Midsouth Shooters Supply for blem bullets.
Otherwise, you will find Hornady Interlok bullets perform as well as Nosler Partitions at 1/2 the price. They are what 'ol Roy used for decades in Weatherby factory ammo. But, Swift A-frames are probably my top recommendation. For extreme long range, the Swift Sirocco is good, but I prefer the flat base Hornady Interloks for general use. Also, the Speer HotCors I've recovered (very few) have held up very well.
I've generally gotten best accuracy with IMR4831, IMR7828, and RL22. But, as I posted earlier, Reloader25 is the standout.
Traditionally, H4831 has been the go-to powder for the Weatherby cartridges. It still works well.
Added; stick with the Norma/Weatherby brass. I've used other (Federal, Hornady, and re-formed Remington 7mmmag brass). They lack the uniformity and case capacity of the Norma/Weatherby cases. If you do use "other" brass, reduce starting loads by another 5%! You can get loaded Norma ammo for close to the same price as empty unprimed Weatherby brass. Other than a few range pickups or gifted cases, the loaded Norma ammo has been my source for Weatherby cases.