What about the bolt fac on a 98 Mauser or the CRF M-70? Harry Shelby's 416 Rigby was mad on a 98 Mauser action. The 416 Rigby is the parent case for the 338 Lapua
I think the main difference is they don't protrude as far and thus will be more rigid. For that bolt face diameter I would prefer PF M70 or the HS Precision as the locking lugs extend to the end of the bolt.
But I think the main issue is you can have the same case capacity with the RUM or otherwise go to the 338/378.
