I found it on a post on 24Hours.....copy of post below. If those shoulder dimemsions are correct it is a very small taper. Might be a misprint and should be .518??

Hornady has confirmed the 375 Ruger's case dimensions to at least one gun scribe, though it differs quite a bit from what Scovil published, as:

Quote:
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Length 2.500"
Rim diameter .532"
Base diameter .532"
Shoulder diameter .528"
C.O.A.L. 3.340"

I was also told that it holds 6 grains more powder than the longer H&H case