Sirois Tool was pleased to have an article published in a recent issue of Defense and Munitions Magazine that highlights our Dow Gage products.

Below is a re-cap of that article:

Dow Gage explains how gun owners and manufacturers can learn to check and measure firearm headspace.

When considering firearm headspace, one source offers this insight: “A practical, descriptive definition of headspace is how well the cartridge fits the gun’s chamber.” The Ballistic Assistant elaborates on this, defining headspace as “the measurement from the breech face to the point or surface that stops the cartridge from moving forward in the chamber.”

Finally, the Palmetto State Armory’s YouTube video, “Headspacing 101,” refers to firearm headspace as the “breathing room” between a rifle’s bolt face and datum on the chamber shoulder, as specified by institutions such as the Sporting Arms and Ammunition Manufacturer’s Institute (SAAMI) and the North Atlantic Treaty Organization (NATO). In other words, headspace is a result of the chamber depth, which is the distance between the end of the barrel and the bolt face in the assembled firearm.

Whether you call it headspace or breathing room, it doesn’t take a firearms expert to understand that a gun’s chamber depth must be precisely sized and aligned to facilitate safe, accurate shooting. In terms of safety, headspace is one of the most important measurements in a gun. Too much or too little headspace around the cartridge can be dangerous, even fatal.

How gun owners check headspace

Headspace should be checked when buying a used firearm or whenever barrel or bolt work is performed. The typical way gun owners and custom gunsmiths measure headspace is with a set of go, no-go, and field gages. To confirm proper headspace, you should be able to close the rifle when the go gage is inserted into the chamber, and you should be unable to close it when the no-go gage is inserted.

However, according to the Palmetto State Armory, the ability to close a rifle with the no-go gage inserted doesn’t always mean the gun isn’t safe to fire. It could just indicate that the gun is used and there’s some minor internal wear. If the gun accepts the no-go gage, checking the headspace with the field gage is the next step.

If the rifle’s bolt closes with a field gage in the chamber, the headspace exceeds the maximum allowed for safe firing. The gun isn’t safe to operate, and it should be immediately removed from service until it has been inspected and repaired by a competent gunsmith.

How manufacturers check headspace The process for checking headspace, or actually chamber depth, for gun manufacturers is more complex. They need to check hundreds or thousands of gun barrels quickly and accurately. Dow Gage offers gages that can be built to check any caliber according to the SAAMI or NATO specifications.

The company has been manufacturing precision gages since 1946. “We’ve provided gaging to the major firearms manufacturers for more than 75 years,” Dow Gage CEO Alan Ortner says. “Our skilled gage makers always ensure that the final product is of the highest quality, and that each gage produces accurate, repeatable measurements.”

The company also serves the U.S. Government’s Military Ordnance industry. Dow gages have been used to check dimensions in military pistols, shotguns, rifles, and automatic weapons.

“Each industry we serve has its own standards for quality and precision, which we take very seriously,” Ortner notes. “When it comes to munitions and firearms, we know lives are at stake.”

In other words, Dow Gage leaves no headspace or breathing room for errors. Neither should you.