Headspace And Gauges

I recently had an ugly experience with excessive headspace when testing a handgun. Not only was the individual handgun unsafe, it seems the design itself was beyond any of the usual fixes. Understanding headspace and its consequences is critical. In this case, the maker did not understand headspace or somewhere in the manufacturing process something went wrong. It isn’t that uncommon.

For example, Lee-Enfield rifles fought in two world wars and are regarded as the most reliable military bolt actions, yet the action was loose enough that handloaders often complain of brass stretching and short case life. This intentional looseness was deemed an acceptable trade off when the rifle was designed and built but isn’t ideal for the enthusiastic handloader. Headspace on these rifles may be adjusted by use of a different bolt but that is a specific fix and we’re looking at the broad picture.

Headspace is the distance from the breechface to a finite point in This is the shipping and storage case. the chamber. Different cartridges demand different points of measurement and need to be understood. Some cartridges are measured from breech face to cartridge case mouth, as is the case of the .45 ACP. Cartridges with rims, such as .22LR and .38 Special are measured by the thickness of the cartridge rim itself. Bottleneck rifle cartridges are measured by measuring the breechface to the cartridge shoulder.

I’ve found headspace is important to accuracy and reliability as well as safety. Too much slop and give in the measurements results in uncontrolled pressure. Headspace is an important determiner of quality manufacture, a gauge of a firearm’s safety, and often an indicator of erratic or eccentric wear. Examine headspace when investigating safety issues, such as a firearm blowing primers.

Other potential problems can be found while checking headspace, such as close examination of the bore and checking for bore restrictions, and chamber condition. A properly-headspaced firearm will contain chamber pressure given quality brass and loads that are in specification though higher pressure cartridges can potentially cause a more serious situation if headspace is out of specification. An essential point of the gunsmith’s kit is a headspace gauge for each individual cartridge likely to be encounter.

These gauges are high quality, hardened steel in the proper dimensions. They area much higher form of chamber check. Simply dropping cartridges into the chamber or cylinder as a check for fit is a good test to ensure reliable function. This doesn’t necessarily mean that headspace is proper but the cartridges will chamber. As an aside, I haven’t found out of spec cartridges among the Big Three, Hornady, and Black Hills Ammunition but have found plenty from manufacturers in the Pacific Rim and south of the border.

As such, they are not service grade loads! It’s essential to use a proper gauge. I’ve seen so-called tests using tape-wrapped cartridge cases, brass rods pressed through the barrel to pull a cartridge forward, and cartridges marked with a Sharpie and chambered to judge by the smudges. These are worthless. Headspace gauges typically come in two dimensions labeled Go and No Go. The Go gauge indicates if the chamber is deep enough and in revolvers measures the length of the chamber.

A chamber that is too short or out of specification may cause spiking pressure. The cartridge case has good expansion properties and may not expand properly in a tooshort chamber. Test if the chamber is too deep with a No Go gauge that should not fit the chamber. These gauges may be used after an obvious problem such as a firing pin piercing the primer, a common sign of a too short chamber. Excess headspace may exhibit an unsupported cartridge case head, possibly

leading to failure or erratic ignition. Cartridges in a too-long chamber may be pushed forward by the firing pin strike rather than the primer being properly ignited. The chamber may hold the case but the powder ignition will not be when intended, resulting in poor accuracy. A primer may back out and gas may flow out even if the load isn’t off specification. Proper extraction may also be adversely affected by a too long chamber.

When dealing with gauges of such a precision nature never force their Clymer gauges are well polished. fit. Do not hammer or tap them into the chamber. The chamber should be perfectly cleaned and degreased before. First, insert the Go gauge and close the action. With revolver, check each individual chamber. If there is any type of binding hesitation, stopping, excess effort, or the action won’t close, the chamber is short and needs to be corrected. Next, insert the No Go gauge.

The action should not be able to close. If so, headspace is excessive and the chamber is too deep. Spanish copies of the Smith & Wesson Military and Police revolver. The revolvers in .32-20 WCF are bored to the point that the cartridge case blows out straight from its bottle-necked profile. Some were evidently intended to accept both the 8mm Lebel and .32-20, however, even those marked .32-20 often give a As an example of improper chamber reaming, I have tested a number of the common problem.

Others in .38 Special accept a No Go gauge in .38 Special. Sometimes these chambers are marked .38 Long Colt but will accept .38 Special and also

Above center: The Manson gauge has given excellent service. Note the good finish. the longer .357 Magnum. This is a dangerous situation found in some old Brothers Hermanos and other makes which were none too strong when new. A catastrophic failure would be the result of firing a Magnum in these chambers. In another example, an eccentric run of .44 Special Colt Single Action Army revolvers was found to accept the .44 Magnum cartridge.

However, it appeared that while the cartridge would chamber and fire, the chamber was tight enough that Below center: Flattened primers mean excess pressure. Headspace may be the problem. I believe the crimp would not have opened and likely would result in essentially a hand grenade at arm’s length. From one of the poorest makers to our finest, I’ve sometimes found the cartridge chamber isn’t always cut properly. It is a more complicated matter to properly check headspace in self loaders.

The chamber must be clean and grease free, as well as the breech face. Remove the extractor as some self loaders will headspace by the extractor instead of correctly headspacing on the cartridge case mouth. Insert the Go gauge and then check for proper lockup. With the No Go gauge the slide should not close over the gauge. Measuring headspace in a rollerlocked rifle, such as the Century C91 or PTR 91, is a different proposition. Century International Arms recomes be used.

The gap between the bolt head and bolt header carrier should be between 0.005 and 0.19. Using standard headspace gauges we close the bolt on a chambered gauge and stop closing the bolt when resistance is felt. If the bolt closes, the length of the datum line to the breech face is greater than the length of the gauge. However, there is some argument that headspace isn’t a function of the locking lugs staying in place.

The position of the roller cams or locking rollers and the inclined position of the locking piece are what will determine headspace in this design. The headspace on CETME rifles is less than the shorter gauge. Closing the bolt on a No Go gauge widened the gap, indicating standard gauges are useful with this rifle. This is due to occasional issues with excess headspace in these actions. As an alternative check, clear the rifle, lock the bolt rearward, and press the trigger to release the hammer. Invert the rifle.

With the magazine well facing up, use a 0.5mm feeler gauge and slide it into the gap between the rear of the bolt mends feeler gaug head and the bolt carrier’s front. This is the maximum proper gap and it should be a tight fit. The 0.25mm feeler gauge should fit between the bolt head and carrier. If the gap is tighter then this, the rifle may exhibit problems with extraction and ejection. AG