Headspace Gauge

A headspace gauge is a precision measuring tool used to verify the critical distance between the bolt face and the chamber shoulder in your AR-15. This measurement, known as headspace, directly affects both safety and reliability. For AR-15 builders assembling uppers or installing new barrels, checking headspace is an essential step that prevents catastrophic failures.

Types of Headspace Gauges

Three types of gauges work together to verify proper headspace:

• GO gauge: Represents minimum SAAMI specifications. The bolt should close completely on this gauge.
• NO-GO gauge: Represents maximum acceptable headspace. The bolt should NOT close on this gauge.
• FIELD gauge: Used to check rifles already in service. If the bolt closes on a field gauge, the rifle has excessive headspace and needs immediate attention.

Why AR-15 Builders Need Headspace Gauges

When you install a new barrel or swap bolt carrier groups, headspace can change. Excessive headspace allows the cartridge to move forward in the chamber, potentially causing case head separation, blown primers, or gas venting into the action. Insufficient headspace prevents proper chambering or creates dangerous pressure spikes.

Quality manufacturers like Forster and Manson Precision produce gauges specifically for 5.56/.223 chambers, typically priced between $30-40 per gauge. While some builders skip this step when using matched barrel and bolt sets, verifying headspace takes under five minutes and provides peace of mind.

Practical Application

To check headspace, remove the extractor and ejector from your bolt, insert the appropriate gauge into the chamber, and attempt to close the bolt. The process requires no special skills, just the right tools. When planning your build on the AR15 Outfitters builder, consider adding a headspace gauge set to your parts list, especially if you’re mixing components from different manufacturers.