Measure Datumm

[gsg5pk]

Can anyone explain why my measure number of Go-Gauge by Forster Datum Dial was not the same number as SAAMI list?

I set the dial hole at .400 which specific for .308 win

The Go Gauge of .308 Win by PTG was 1.630
The No Go-Gauge of .308 Win by PTG was 1.636

But I got these number

 

[Nomad47]

Does the .400 hole on the Forster gauge measure .400" and is the edge of the hole VERY sharp. .009" isn't very much and I think the various headspace gauges are meant more for comparison than for actual measurement. For example, the gauge would be very reliable for telling you when you have bumped shoulders .002" on your brass. And it would be good for comparing go gauges. But is it measuring at the .400 datum point or the .402 datum point?

 

[BoydAllen]

+1

 

[bigedp51]

When I was in the military and on my first datum, I never complained if the hole was on the small side. :

 

[jsn]

Is there a radius on the end of the Forster .400 hole? If so there's your .009. My Stoney Point tool is the same way.