While I like that you are going big. The .50 Beowulf is actually the largest that will fit that frame. Yes you only get 7 shots, but it is the biggest.
https://www.shopalexanderarms.com/50_Beowulf-Uppers.html
Happy hunting!
Yes, it is indeed the biggest that will fit.
But will it reach out to 800 yards and still be accurate?
Good argument to be made for the .468 SOCOM, as well.