Is this going to be a LRH or UNP?
If LRH, someone is finally gotten to the right caliber. Why try to control all that recoil?
I have no experience with the 22 BR but Joe B. had good luck with the 22-250 which if even more overbore so it should work. I have won matches both with NOE 22572 RN and 22779 SP or very similar bullets, but never at 200 with the RN bullet. A good wind doper coulld probably do it, but not me. All other 22 molds on the market have BCs lower than whale dung and would be a real challenge if there is any wind.
Now that NIE and LBT are apparently out of business and none of the custom mold maker can and will make such bullets NOE is the only source that I know of. If there is one out there, I have a job or two for them. Please speak up.
The 72RN will stabilize in a 10" twist and the 79SP in a 9" twist but an 8" gives more margin of stability. A 9" twist will stabilize a 22 bullet 0.9'" lonb at CB speeds, -- but just barely.
I have had good luck with alloys from 1:25 to linotype but have decided that soft is easier to get good accuracy in factory chambers. For a custom gun with swaging die cut with the same reamer as the throat, I assume that harder alloys would be better.
I have found good loads with everythng from TiteGroup to Varget but have settled on fast powders for my soft bullets at low speeds. The opposite may be true for hard bullets in a custom chamber.
I am a primer skeptic. I have never seen any difference in average group size when comparing primers if all the powder burned. I have used pistol, regular, and magnum primers and all seem to produce good accuracy.
Jack Harrison came in second in production class at the 2019 CBA nationals with a score that would have won in most years but Gerry (super man) Bottiger was shooting in that class. He wss using the NOE 80 grain bullet. You may want to get his advice.
PS If that XP 100's bolt hasn't already been converted, why not a 222 or 223. Laupua makes super cases for both?