To define each type, we’re going to use headspace as a verb and refer to how a cartridge “headspaces.” In other words, different cartridge and chamber designs use different brass case and chamber features to lock the cartridge in place, leaving just the right amount of space between the cartridge base and breech face.īefore we get into the different headspace measurement types, let’s clarify some supporting terminology. There are three and a half approaches to locking a cartridge in the proper place in the chamber. Or worse, the cartridge might just flop around and stay out of reach of the firing pin altogether. Without that, the firing pin might simply push the cartridge forward without making a big enough dent in the primer to cause ignition. Something has to hold the cartridge in place before it’s fired to keep it in exactly the right position. When I say fit I’m talking about the locked and loaded positioning. To do that, we first need to understand that different cartridge designs fit into chambers in different ways. Now let’s talk about what headspace technically is and how it’s measured. Rifle headspace supposedly is a mysterious thing few people can figure out. That’s the dimension that headspace impacts. So, there always has to be a little bit of play between the breech face and the cartridge base. The case also stretches just a hair lengthwise. The circumference increases and the case temporarily presses against the chamber walls. Also, cartridge cases expand in two dimensions when fired. A cartridge can’t exactly match the length from the bolt face to the limiting forward portion of the chamber because there would be no wiggle room to allow for loading, unloading, or a bit of fouling. While not the technical definition, you can think of headspace as the free space between the breech face and the cartridge base once it’s loaded in the chamber and the bolt or slide is closed. If we discuss what it implies and what it actually means separately, I think it’s a lot easier to digest. The concept of headspace and its ramifications is pretty simple. If you’re not a gunsmith or avid reloader, the importance of headspace can seem like a daunting topic. When customers buy a used firearm, especially a military surplus model, everyone’s advice is to check the headspace. Rifle headspace is one of those topics that, in reality, is not nearly as mysterious as it seems.
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