Be aware, if I am reading the Midway description correctly, that when using the field gauge, if the bolt closes when the gauge is installed, it's dangerous to shoot.
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If the action closes when this gage is inserted, then the firearm may not be within acceptable maximum headspace dimensions and should be examined further by a knowledgeable gunsmith.
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They have other gauges available:
# Go Gage:
# Ascertains correct headspace dimensions by duplicating the minimum allowable distance, from the case head (or boltface) to the datum line of the cartridge's shoulder, allowed within the chamber to secure a loaded cartridge and allow the breech to be closed in a safe manner for firing.
# If the firearm locks up in battery when the gage is inserted, then it is within acceptable minimum headspace dimensions and may be used.
No-Go Gage:
# Duplicates the distance over the maximum allowable, from the case head (or boltface) to the datum line of the cartridge's shoulder, allowed within the chamber to secure a loaded cartridge and allow the breech to be closed in a safe manner for firing.
# If the firearm locks up in battery when the gage is inserted, then it is not within acceptable maximum headspace dimensions. The firearm should not be used and should be examined further by a knowledgeable gunsmith.
Field Gage
# Duplicates the maximum allowable distance, from the case head (or boltface) to the datum line of the cartridge's shoulder, allowed within the chamber to secure a loaded cartridge and allow the breech to be closed in a safe manner for firing.
# If the firearm locks up in battery when the gage is inserted, then it is at the maximum acceptable headspace and should be examined further by a knowledgeable gunsmith.
