Hopefully the explanation below will be of some help in putting unfounded concerns to rest.
- The "Go" Gauge is used to make sure that standard factory loaded ammunition will fit reliably. Insert the Go gauge in the chamber and close the bolt. If the bolt won't close or closes with resistance, you may have the barrel screwed in too tight. Your headspace is too tight and won't fit factory loaded ammo reliably.
- The "No-Go" Gauge is where things can get confusing. The SAAMI spec allows up to .010" headspace. Custom re-barrel shops usually want to fit headspace closer than that, so they order closer fitting No-Go gauges. Forster's No-Go gauges allow only .004" headspace. Manson's No-Go gauges allow only .006" headspace. So if your action closes on either of these No-Go gauges, it doesn't mean you have excess head space... Only that it's more than the gauge allows.
- The "Field" Gauge is used to make sure that headspace on a factory installed barrel is not too long to support factory loaded ammo. A Field Gauge checks SAAMI spec for maximum allowable headspace of .010". If your action will close on the Field gauge, it probably has excess head space. Actually anything between the "GO" and the "Field" dimension is within SAAMI specs. We don't offer the Field gauge primarily because our gauges are intended for customers who are installing new barrels on Savage rifles and getting the install close to the NO-GO dimension is the best approach.
Practical Considerations When Using Headspace Gauges
- Ideal Headspace is when the bolt will close on the GO gauge but will not close on the NO-GO gauge. You might as well get it perfect if you're installing the barrel yourself.
- Special Circumstance #1 - When headspace gauges are not available, full length sized, not yet loaded cartridge brass is sometimes used to custom fit the headspace by trial and error. Re-barrels done this way may fit your handloads fine but may not fit factory loaded ammo.
- Special Circumstance #2 - A rifle with *barely acceptable headspace may be perfectly manageable by reloading ammunition with brass that is custom fit by partial full length resizing or neck sizing. For example, if you're using headspace gauges to check a factory barreled rifle, and the bolt closes with slight resistance on the No-Go gauge, it is not necessarily excessive headspace... Just more headspace than would be considered ideal. (There's actually a third "Field" headspace gauge that's the definitive No-Go headspace indicator. We recommend the closer fitting NO-GO gauge for installing a new barrel).
- Special Circumstance #3 - TC Encore and Contender barrels can give a false reading with Go and No-Go gauges if you don't understand the locking mechanism that draws the barrel down into full battery. The spring loaded locking bolt engages the frame and can "click" shut and latch the action closed well before it extends completely... Giving the impression it closed on a headspace gauge when in fact it didn't. (A TC Encore or Contender locking bolt has an angled engagement surface and must extend fully in order to draw the barrel completely down into battery.)
Multiple Chamber Compatibility...
Many headspace gauges will work on more than one chamber.
- 223 Remington gauges work on .223 Rem and 6x45.
- 243 - 308 Family gauges work on .243 Win, 260 Rem, 7-08 Rem, 308 Win, and 358 Win.
- 6.5 Creedmoor Gauges work on 6.5 Creedmoor and 6mm Creedmoor
- 6.5x55 Swede gauges work on the 6.5 x 55 Swedish Mauser.
- 280 Remington gauges work on the 280 Remington.
- 284 Family gauges work on 284 Winchester, 22-284, 6-284, 25-284, 6.5-284 Norma, 270-284, 30-284, and 35-284.
- 30-06 Family gauges work on 25-06, 6.5-06, 270 Win, 30-06, 8-06, 338-06, and 35 Whelen.
- Rimmed or Belted
-300 Mag gauges work on 257 STW, 257 Wby, 264 Win, 6.5 Rem Mag, 6.5 STW, 270 Wby, 275 H&H, 7mm Rem Mag, 7mm Wby Mag, 308 Norma Mag, 30-338 Win Mag, 300 H&H, 300 Win Mag, 300 Wby, 8mm Rem Mag, 338 Win Mag, 340 Wby, 350 Rem Mag, 358 STA, 375 H&H, 416 Rem, 458 Win Mag
- 30-30 Winchester gauges work for 375 Win, 7-30 Waters, 6.5 BRM, 6 BRM, 30 Herrett, 219 Don Wasp, etc.
We hope that helps you with your barrel installation or headspace testing.