Headspace Of Reloading Brass
- Part 1
In an effort to look at certain reloading fundamentals for rookies, we will take a look at the importance of measuring headspace and accurately bumping the shoulder on your reloading brass. But keep in mind that this article is a “why to” not a “how to.” The how to will come in the instructions with whichever measuring system you decide to go with, plus a reputable reloading manual.
WHEN TO CHECK HEADSPACE: Headspace of the reloading brass should be checked after performing any action work such as chambering a barrel, changing a barrel, or changing the bolt. You should also check it on any used gun you purchase at a gun show, a store, or from a friend - before you fire it.In most cases, a brand-new rifle will have been checked for headspace, and maybe even test fired, before it leaves the factory. Even so, mistakes sometimes do happen at even the best-run factories, so it really doesn't hurt to check the headspace on a new gun, right out of the box.You can see the critical importance of correct headspace. What you don't know can hurt you. But how do you know if your gun's headspace is correct? Look for part two of this series on headspace and the fundamentals needed for proper reloading brass.
Why Measure Headspace: Headspace is one of the most critical dimensions on your firearm. It is the distance from the bolt or breech face to a point on the chamber; the exact location of that point varies from one type of cartridge to another. For a rimless bottleneck rifle cartridge, that point is where the shoulder of the case rests against the shoulder of the chamber. For semi-auto pistol cartridges, it's a ridge at the front of the chamber that the mouth of the case rests on. Rimmed cartridges like .38 Special and .45-70 are retained by the rim resting on the back of the chamber, just as belted magnum rifle cartridges "headspace" with the belt resting on a shoulder in the chamber.
THE PROBLEM(S): When the primer ignites the powder in the cartridge of the reloading brass, enormous pressure builds up rapidly and makes the case expand against the chamber walls to create a seal. This keeps the hot gases from escaping, except by pushing the bullet out of the case mouth and down the bore. At the same time, the base of the case also expands backward and presses against the bolt or the breech face.
Excessive Headspace: Excessive headspace in the reloading brass casing can lead to bulged cases or even outright failures - cracks, case head separation, and splitting of the case neck. It can also because light primer strikes, failure to fire, primers popping out of the primer pocket, and of concern to reloaders, shortened case life. A catastrophic case failure can allow hot gas and even bits of brass to escape from the receiver and injure the shooter or bystanders.
Not Enough Headspace: Insufficient or excessively tight headspace can be just as dangerous. It can prevent the gun from going into battery, leading to a failure to fire or damage to the case caused by attempting to force the breech closed. Forcing the breech closed can jam the case neck too far forward, causing it to grasp the bullet too tightly, which delays the release of the bullet and leads to excessively high chamber pressures.