I’m going to ask an unpopular question but are you cleaning that gun? I have to clean my PRC and 243 AI, they both develop carbon rings. Carbon rings will definitely spike pressure.
Are you talking about the factory standard chamber? I'm not sure I didn't check when I got my gun. You can load up a dummy round and send it with the gun to the gunsmith and he can chamber/throat it however you like. My loaded round with the 108 comes out at approx. 2.9"
I have a friend that has killed at least 30-40 deer over the last several years with a 22-250 and 53 grain Berger varmint bullets that has recovered every one of them. Maybe my buddy is a better shot??
Hodgdon has data available for BLC-2, 335, and Varget. There are more options but somewhere to start with what you have.
https://hodgdonreloading.com/rldc/
The 243 AI has significantly more case capacity thus requiring a slower powder, barrel is 22". H4350 would be too fast if trying achieve the case fill I am. So yes, different cases with different powders often create discrepancies in volume.