You can figure +250 fps more out of a 257 Weatherby with no freebore. I hand load my ammo and would never even consider shooting a factory round.
In a chamber with no freebore, you can not shoot factory round, bullets have to be seated for that chamber.
Accuracy is in the high 2's and low 3's for three shot groups using 100g nosler partitions. Sierra 100g spt bt are a little bit better with velocity at 3750-3850 depending on the bbl. I do believe that 3 groove bbls are faster than 6 groove bbls, at least on the bbls that I have had.
Ive used IMR4831 only with the Speer 120 SPBT. The load is in the Speer book, max was max in my Lghtwt. Excellant accuracy though. I have not shot the 110's only the 115 Baltips w/H1000. The 100 Sierra's w/RL-22.
All I can contribute to this is that I have a 25'06 Ackley and use 100 Grain Noslers with 57 gr. of R22. (barrel length is 28½) Comparing my velocity (3650fps) with most published data on the 257W, my load will run right with it, but not with the heavier bullets. And, this is with 10/12 grains less powder than the Weatherby; which certainly has more potential, set up correctly.
Yeah, I have dumped a few Nevada coyotes with this gun. I always have it handy for the long ones; this rig makes it almost routine. Doug did a heck of a job. Now, it's a bit of a shame, all he works with is his Paints. (horses) He doesn't hunt, at all.