8X57 Mauser (8mm Mauser)
Chamber Headspace Variation and Measurement
SAAMI’s current Chamber and Cartridge drawing (ANSI standard) shows a 19° shoulder angle in the chamber. The earliest revision of this print showing 19° is dated April 21, 1980.
The shoulder angle in the 8 x 57 Mauser, however, hasn’t always been 19°.
A SAAMI/Winchester Repeating Arms print, New Haven, CT, dated November 12, 1938, shows a 20° 48’ shoulder angle. The last revision made on this 20° 48’ angle print is dated July 9, 1947.
It appears that the transition from the older 20° 48’ shoulder angle to the current 19° shoulder angle did not happen suddenly. Discussions with gunsmiths and collectors indicate that there may have been a 15 to 30 year period during which firearm chambers were manufactured to both shoulder angles.
Measurement and Gaging Implications
Headspace gages that are made to the current 19° shoulder angle will not properly check older 20° 48’ shoulder angle firearms. Because of the shoulder angle difference, a 19° gage does not match to the datum measurement point of firearms that are chambered to 20° 48’. A 19° headspace gage will appear as if it were longer because the 19° shoulder angle will contact the bore of the chamber before it contacts the chamber’s datum point.
Determine whether the chamber of a particular firearm is made to the current 19° shoulder angle or to the older 20° 48’ shoulder angle. This may be done by making a chamber casting using CERROSAFE® or a similar material.
Once the shoulder angle is confirmed, then obtain the correct headspace gages. Forster manufactures distinct gages for both the current standard 19° shoulder angle and for the older 20° 48’ shoulder angle chambers. Order numbers for the older 20° 48’ gages are:
- GO Gage: HG8mmoldG
- NO-GO: HG8mmoldN
- FIELD: HG8mmoldF