Three lengths of Headspace Gages are available per caliber:
ªGO length — This checks the rifle to see that the chamber will accept the cartridges made to
maximum SAAMI specifications.
ª NO-GO length — This is used by most gunsmiths as a maximum headspace gage when
chambering a rifle’s headspace dimension. If a rifle closes on a NO-GO gage, it may have
excessive headspace. If a rifle closes on a NO-GO gage, it may still be within the SAAMI
Rifle Chamber tolerance. Next, it should be checked with a FIELD gage.
ªFIELD length — If a rifle closes on a FIELD length gage, its chamber is dangerously close
to, or longer than, SAAMI’s specified maximum chamber size. This is the longest of the three
Insert the proper gage into the action. Attempt to close the bolt on the gage. CAUTION — Never
force the bolt closed on a gage. A rifle with correct headspace should close easily and without feel
on the GO gage, but should not close on the FIELD gage. If it does close on the NO-GO gage, but
not on the FIELD gage, the rifle may still be serviceable. However, it is not advisable to use it for best
accuracy with factory ammunition. CAUTION — Any rifle that will close on the field gage may have
dangerously excessive headspace and should not be fired under any circumstances.
GO, NO-GO, and FIELD length Headspace Gages are available in the following for rimless calibers:
22 PPC, 220 Swift, 222 Rem., 222 Rem. Mag., 22-250 Rem., 223 Rem.,
243 Win., 244 Rem., 250 Sav., 25-06 Rem., 257
Rob., 270 Win., 6mm PPC, 6.5 x 55 SKAN, 6.5 x 55 Swede,
7mm-08 Rem., 7mm Mauser, 280 Rem., 284 Win., 30-06, 308 Win., 8mm x 57 Mauser, 358 Win.