I have a Stoney Point Headspace gauge, that I use on all my other cartridgecases. I would like to be able to adjust my 416 rigby sizing die using the same gauge, but I don't know the datum line diam. on the case shoulder of a 416Rigby, and to be able to adjust the headspace correctly, I need exactly that.
Please help me out.

Thanks in advance

According to Art Alphin's book, the Rigby case measures .540" at 2.353" from the bolt face, and .447" at 2.400" from the bolt face.

Hi Recono

Yes it does, but what I am looking for is the so called datumline dia. which is in the middle of those reference points. I am not a math monster so it would be easy for me, if you or someone else knew the exact value of that diam.

Hi again Recono

It seems that I am a "mathwizard" after all.... It also seems that I gave up too soon. the datum line dia should be
= to (.540-.447/2)-.540

It is not wrong what they tell you in the army....
That When you leave it, you can do twice as much as you thought you could, and ten (10) times as much as your mother thought.