September 9th, 2021
This illustration shows the headspace measurement of the popular.308 Winchester cartridge. It headspaces on one side. Image copyright 2015 Ultimate Remo. In this Brownells Tech Tip Steve Ostrem, Brownells gun tech explains what headspace means and why it is so important for almost all firearms. Even if your rifle shooting skills are advanced, this video will refresh your knowledge on headspace measurements and correct use of “GO” and “NO-GO” gauges.
Definition of Headspace
Headspace in firearms is the distance from the end of the chamber that stops forward movement of the cartridge (the datum refer) to the bolt’s face. Different cartridges have different datum lines. 5.56x45mm NATO ammunition headspaces are located at the cartridge’s shoulder, while.303 British headspaces are located at the cartridge’s forward rim. A short headspace can cause ammunition not to chamber properly if it is not in specification. Headspace that is too large can cause ammunition to not fit as designed or intended. The cartridge case could also burst, causing injury and damage to the firearm. (Source: Wikipedia
Too Much Headspace Can Cause Problems
Excessive headspace can lead to: failure to fire, light primer strikes, failed firing, bulged/blown case, case separations and split shoulders. Excessive headspace can cause catastrophic failures and serious injury, such as case ruptures. This is why headspace is so important.
Too little headspace can cause problems
Too much or too little headspace can prevent the firearm’s battery from being charged. This can lead to the failure to fire the cartridge case or a malfunction in the firing mechanism. Too little headspace can cause various feeding and function problems, even though a round can still be chambered (with effort).
Headspace Gauges
A set of two headspace gauges is used to measure headspace. One is a “Go” gauge and one is a “No Go” gauge. Headspace gauges look similar to the cartridges that are used to headspace the chambers. They are usually made of heat-treated steel. A gunsmith must have both a “Go” gauge and a “No Go” gauge in order to properly headspace a firearm. The “Field” gauge is used in the field to indicate the safest headspace. This gauge is important because the bolt and receiver can wear, the bolts and lugs may compress, and the receiver might stretch. All of these factors cause the headspace to gradually increase over the “factory specs”, as measured by the “Go” and “No-Go”. A bolt that closes on “No Go” but not “Field” is dangerous to fire and could cause cartridge malfunctions. Source: Wikipedia
Brownell’s article Headspace gauges and how to use them explains more. This explains, among other things, the relative lengths for “Go”, “No Go”, and “Field”, respectively. The “Field”, in fact, is the longest. “The GO gauge corresponds with the SAAMI minimum chamber size, while the FIELD gauge matches the maximum chamber depth or slightly less. The NO-GO gauges are a length in between minimum and maximum that technically is a voluntary dimension. A firearm that closes on a NO GO gauge but not on a FIELD can cause inaccurate firing and short cartridge life.
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Tags: Brownells. Chamber, Chambering. Headspace. No Go. SAAMI. Shoulder Data.
