I didn't read this whole thing and may have suggested this before but I would try the 128 Hammer Bullets

https://hammerbullets.com/product/257-cal-128g-hammer-hunter/

Other Hammer bullets have shot well for me and I am using the 103s in a 257 Weatherby with good luck. One thought on the Black Jack bullets since they are made by Sierra most long range shooters would use a meplat uniformer on the Match Kings.

BiBullets will do custom bullets as well as some others but will have a 1-5,000 minimum so maybe a group buy? Hammer will also do custom orders but not sure of their minimum. I would like to see the maximum for 1-10 twist bullet seems like they could go heavier than the 103.

"When you disarm the people, you commence to offend them and show that you distrust them either through cowardice or lack of confidence, and both of these opinions generate hatred." Niccolo Machiavelli