I'm no expert when it comes to the magnum cartridges, but given the body diameter on the Nosler's I'd strongly lean towards a large shank. I know there are guys here who have built WSM's on small shanks, and all the .300WM and .338WM rifles built prior to 2001 (and maybe after?) were on small shanks.
The other question is what magazine are you going to use? I imagine one for the .375 Ruger would be the closest, but you would still have to modify the feed lips for the larger diameter case body.
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