You mentioned interest in LR shooting. Id pick a case that could push the 300 class bullets at a reasonable speed.

If hes an avid handloader, the 338-375 Ruger would likely fit the bill.

Is a 375 R Howa barreled action available? Swap with his XCaliber contoured to Bart 3ish range. McMillan Sako Hunter.

Or just 338 WM it.

“Life is life and fun is fun, but it's all so quiet when the goldfish die.”