I don't think you really want to do that...
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On the right is a 20X seated where it should be, with the body/boat-tail junction above the case neck/shoulder junction, for a chamber with 0.170" freebore (OAL >3.1"). Even with that long of a freebore, and a 28-30" barrel... MV is around 2630-ish for the 'low' node - the one that won't wreck your brass in a couple firings.
On the left is a 20X seated down to 2.850" OAL.
And for the sake of argument/discussion... on the one hand, I consider the Berger load manual largely useless, as every single load is @ 2.800" - even for a 230gn Hybrid in a .308 Win. Sierra somehow figured out how to have 'bolt gun only' or 'specialty gun only' load data for the stuff that really needs a specific long freebore setup, but not Berger
That said, this particular bullet came out well after the Berger loading manual. You might be able to fudge the numbers from a similar bullet, but then I'd recommend calling Berger/Lapua/Vihtavouri. Their tech support guys will be able to give you some base line data to at least start with.
Personally, I think it's a bad idea, and a waste of a really good bullet in a totally wrong application, but I've only been shooting them since before they were commercially available...