This link is from Foster Gauges: http://www.forsterproducts.com/resource ... surements/
Was thinking of purchasing a MG34 barrel for a spare and don't have any 8mm headspace gauges.
In my search for gauges, I got this info. Old 20° 48” shoulder angle was changed to the to the current 19 ° shoulder angle. Current 19° headspace gauges will appear as if they are longer. In that case your Go- Gauge will not close if its set right on the money and you may think that you have to tight of a head space.
The earliest revision Foster has of this 19° SAAMI print is dated 4/21/1980.
You have to call Forster directly for the 20 degree gauges.
Order numbers for the older 20 48 gauges are: GO Gauge: HG8mmoldG , NO-GO: HG8mmoldN , FIELD: HG8mmoldF
Read the link, it's more detailed.
Just passing on info that in my old age I'm learning.