When we manufacture our headspace gages, we base nearly all dimensions on SAAMI standards. These measurements are the industry reference point for most modern firearms.
However, not every cartridge began its life in the SAAMI era—and sometimes the original military specifications simply don’t match today’s SAAMI dimensions.
A perfect example is the .303 British.
The original military standard for .303 British used a Field length of .074″, which is actually longer than the current SAAMI maximum.
Because so many shooters and collectors still run original Enfields and other pre-SAAMI rifles, we’ve listened closely to what customers need. That’s why, by customer request, we offer a special .074″ military-spec Field Gage for the .303 British.
303 Brit Mil Field
When it comes to safety, if your rifle closes on a Field Gage—especially on older military rifles—we strongly recommend confirming with your gunsmith before firing. It’s always better to double-check than to risk unsafe headspace.
For more details on proper headspace use and general instructions, click here to review our guide.
If you have questions about gages, specs, or what you need for your build, we’re always happy to help.