416 Rigby datum diameter?

[MagnumManiac]

Hi all,
I'm hoping someone can help. I have the SAAMI drawing for 416 Rigby but cannot find what diameter the datum is. The headspace is listed but no reference is made of where it's measures from.

I'm looking at making my own comparator sleeve to use in the Hornady Lock 'n' Load Headspace Gauge.
I was thinking a .500" hole would do it.

What say you?

Cheers.

 

[MagnumManiac]

After considerable perusing of the SAAMI specs, I believe that the dimension I need is .496"...this appears an odd number to me, as all other datum points are a whole number like .420", .400" & .375" etc.

Please set me straight if I am incorrect.

Cheers.

 

[jrock]

You don't really need to be exactly on the datum if your goal is to just measure how much you bump the shoulder back. Just measure the diameter about half way down the shoulder and use that number. I've seen guys us pistol cases as gages. Its just an arbitrary point you are using to measure from.

 

[MagnumManiac]

You don't really need to be exactly on the datum if your goal is to just measure how much you bump the shoulder back. Just measure the diameter about half way down the shoulder and use that number. I've seen guys us pistol cases as gages. Its just an arbitrary point you are using to measure from.

Thanks for your reply.
I realise that it does not need to be precise, but the shoulder on a 416 Rigby is very small and difficult to measure accurately.
I also have a 338/416 Rigby Improved with a datum diameter that is unique and had to turn up a comparator for.

Cheers.

 

[jrock]

yes .496

 

[MagnumManiac]

yes .496

Thanks Jrock.