A note from Dave Kiff on Pacific Tool headspace gauges:
Our firearms headspace gauges are made to many different lengths, but European Proof House (CIP) and The United States Standard (SAAMI) come in the following lengths (the SAAMI Min Go gauge, along with custom chamber Go gauges, start with the headspace gauge being ground to absolute min per voluntary standard by SAAMI or CIP):
Go gauge is Min SAAMI, CIP or custom bolt face to shoulder angle datum length size and is recognized as the absolute minimum length.
Max CIP is +.0039 from the Go and is enforced by most European countries as the absolute Max No-Go for chambered rifles, used by all European Proof House for Max chamber length.
No-Go is the +.005 from Min Go. The standard No-Go is the voluntary Precision Gunsmiths Max and it is used by gunsmiths in other non CIP countries as the voluntary No-Go and not usually recognized as a SAAMI nor CIP gauge.
Max SAAMI gauge is at +.010 from the SAAMI Minimum Go. This gauge is called Field gauge by a lot of the civilian and military manufacturers.
Here is a list of the common length gauges that can be purchased and requested by customers. The list goes as follows:
Go gauge, Min CIP, Min SAAMI
CIP Max is +.0039 from Min CIP or Min SAAMI Go
Voluntary precision gunsmithing No-Go (ours +.005 from Min Go)
Max SAAMI Field gauge is +.010 from SAAMI Min Go
We sell a gauge set for $99.00 that consists of a Min Go, +.005 No-Go and a +.010 Max SAAMI and Field gauge. Otherwise, you can purchase the SAAMI, CIP or Wildcat gauge in different lengths. We also grind an 11 piece gauge set in .001 increments that have a -0 to +.0002 tolerance. I have a lot of customers calling me about their hand guns or gas guns closing on the No-Go, such as an AR-15 closing on a standard No-Go gauge. Remember most gas gun manufacturers run their headspace a little longer for rapid firing and to have the ability to perform with a dirty chamber.
If a precision gunsmith chambers a bolt action barrel or an AR for you, he will most likely ream until the bolt just closes on the Go, but a +.005 No-Go should work as a No-Go. Remember, most manufacturers chamber their AR-15’s and other gas guns to +.002 for Go from SAAMI Min to +.007 from SAAMI Min for their production No-Go. I always check my gas guns with a military 11 piece incremental set of gauges to find out the true depths of the headspace. Example: A Min 223 Rem, 5.56 Nato, 223 Wylde or 20/223 practical Go gauge is 1.4636 to .330 shoulder datum. The 223 Rem No-Go is 1.4696 to .330 shoulder datum (for most bolt actions and precision chamber barrels). The military Max and SAAMI Max Field gauge is 1.4736 to .330 datum and some chamber their gas guns to the Max SAAMI Field of +0.10.
I hope this helps and any time you need help on headspace gauges or custom reamers, please feel free to call me with your questions or needs.