headspace?

[Rick W.]

i

[Kyrie]

Hi Rick,


Your comments and concerns re headspace are well taken. Here is a good basic introduction to headspace:


http://www.cruffler.com/trivia-October99.html


All cartridge firearms have an acceptable range of headspace, including Lugers. The standards for headspace here in the US are set by SAAMI (Sporting Arms and Ammunition Manufacturer's Institute). In terms of the use of headspace gauges, in essence the action must both close on a Go headspace gauge and not close on a Field Reject headspace gauge.


There are no standards for â??No-Goâ?� headspace or the No-Go headspace gauge. The No-Go headspace gauge is sometimes called a â??reloaderâ??s headspace gaugeâ?� because it indicates whether the firearm is safe to use with ammunition assembled from used cartridge casings. It is also frequently used in place of the Field Reject headspace gauge to check the headspace on used firearms to buy a little added protection over that offered by the Field Reject gauge.


So called â??gunsmithsâ?� who use cartridge cases to set or check headspace are a menace. Headspace cannot be accurately verified by the use of a cartridge case. In setting or verifying headspace measurements must be taken to a thousandths of an inch (0.001 inch). The length of cartridge cases from their case head to the place where they make contact with the chamber (case mouth for the 9x19 Parabellum, a point of the shoulder for 7.65x21 Parabellum) is almost always less than the minimum headspace dimension for a firearm chambered for that cartridge - and varies considerably. Additionally, cartridge cases are soft and easily compressed. Even if one were lucky enough to find a cartridge case with a length that was at either minimum or maximum headspace, it would conform to the dimension of any improperly cut chamber during and after one use. Headspace can only be checked with a correctly manufactured headspace gauge.


Shooting a firearm with unacceptable headspace can result in the injury or death of the shooter, and of bystanders. Insufficient headspace can result in truly horrible chamber pressures; excessive headspace can result in case failures and the release of very hot and very high pressure gases. In cases of excessive headspace, even if the cartridge case survives firing, the bolt, frame, or slide can be cracked by slam back. Ammunition that is too short from case head to the forward point where it should come into contact with the firearmâ??s chamber mimics excessive headspace. Ammunition that is too long from case head to the point forward where it should come into contact with the firearmâ??s chamber mimics insufficient headspace. This is why correct setup of the resizing dies used by handloaders is so important.


Headspace is something of a complex subject, and Iâ??ve just brushed over the very basics. If you would like to get into more detail (including where to obtain headspace gauges) drop me a note off-list.


Best regards,


Kyrie

[Johnny Peppers]

General Hatcher has a very good discussion of headspace in his book, "Hatcher's Notebook". In it he explains the different problems with different types of cartridges relating to headspace. He tells of firing .45ACP cartridges in a Webly & Scott Selfloading Pistol. With this combination there is approximately 1/8" of excessive headspace. If the cartridge is dropped into the chamber, the pistol will not fire as the firing pin cannot reach the primer. If the cartridge is loaded from the magazine, the extractor holds the cartridge against the breech face and the cartridge fires normally. He did the same thing with a 9mm Luger and P38 by firing .380 ACP cartridges in them. If the cartridges were loaded from the magazine, the cartridges fired normally but would not extract due to insufficient power to operate the toggle assembly or slide.

.45ACP cartridges may be fired in .45 Colt revolvers as long as "half moon" clips are used to hold the cartridge against the face of the breech. In this case the actual excessive headspace is somewhere around .05 inch.

While I don't recommend anyone firing a questionable firearm before having it checked by a competent gunsmith, Hatcher's observations are interesting.