How To Check AR 15 Headspacing

This guide briefly goes over how to check AR 15 headspacing for firearm safety purposes. It's important to check the headspace for safety every time you build an AR, replace a barrel, install gas tube or change a bolt carrier group.

Most of the time, things will be fine, but it's better to be safe than sorry.

This content is strictly for educational purposes only. We are NOT responsible for any injuries or damage to your guns if you didn't check the headspace properly.

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What Is AR 15 Headspacing

ar15 headspace

The Headspace is the distance between the base of the bullet and the head of the bolt. 

Headspace, the gap between the bolt or breech and the chamber's specific point, differs with each cartridge type. Always take a moment to verify the headspace with every build or part replacement to prevent these risks.

As the cartridge enters the chamber, it's this shoulder that should meet the chamber's machined counterpart to set the headspace. Proper headspace allows the bolt to move forward and the locking lugs to engage without over-compressing or under-supporting the cartridge.

Out of spec casing length or barrel extension can cause issues.

How To Check AR 15 Headspacing

go and no go gauges

Checking AR 15 headspacing is all about safety, performance, and getting the most out of your firearm. So next time you're at the bench, take a moment to check your headspace - your rifle will thank you for it.

Incorrect headspace can lead to dangerous problems, including catastrophic rifle failure. Issues like case separations, blown primers, ejection issues, and misfires often stem from headspace errors.

If headspace is too loose, upon firing, the cartridge can move forward, and the subsequent pressure can over-expand and snap the brass, leading to a potentially dangerous situation.

If it's too tight, the bolt may not close fully, leading to a failure to fire or difficulty in extracting a live round.

Use No Go Gauge

no go gauge ar15

A Go and No Go gauge matches the biggest cartridge size allowed. When the bolt shuts on the go gauge, the headspace is likely fine. But if it closes on the no-go gauge, that's not good—it means there's too much space. This won't make your gun unsafe right away, but it will damage your brass cases because they'll stretch to fill the space.

Most shooters might not worry about damaged brass, but those who reload their ammunition do. The process of reloading involves stretching the brass, reshaping it, and stretching it again, which is tough on the cases.

Given the shortages of ammo, it's smart for all of us to care about keeping our brass in good shape. You might not reload your own ammo, but chances are, someone else will want to use the brass you've fired at the range.

Tips For Checking AR 15 Headspacing

ar15 barrel chamber
  • Mil-spec parts should have very little headspace difference, at most two thousandths of an inch, which is okay.
  • If you check headspace, do it on just the barrel and bolt to keep things simple.
  • If the headspace is too tight, you can use a reamer to enlarge the chamber. However, do not ream if the chamber is chrome-lined or nitrided, as it could damage the finish.
  • Factory ammo and chambers usually match up within safe limits. However, for handloaders seeking precision, maintaining tight headspace is vital. It ensures that the cartridge presents the bullet to the rifling consistently every time.
  • Avoid pushing the shoulder back too far. Instead, size the brass just enough to allow the bolt to close without affecting the shoulder. This means setting up your dies to resize mostly the neck, not the shoulder.
  • They use a "go gauge" to see if the bolt closes right. If it does, that part is good.
  • Then they use a "no-go gauge" to make sure the bolt doesn't close too much. It doesn't, so the headspace is tight and safe.

Common FAQ

Can you mix and match barrel and BCG?

ar15 bcg bolt head

You can mix and match barrels and BCGs in an AR-15, but it's important to check that the BCG is properly headspaced with the new barrel. Without verifying headspace when you swap parts, you might encounter problems due to incorrect headspace.

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