What is "headspace", and how does it affect your rifle or firearm? Unless you consider the Big Book of Ballistics a good read, I am going to try to break it down and simplify this for you.

DEFINITION

Headspace, in the firearms world, is a term of measurement. It is an especially important measurement for reloaders
. An easy way to describe this measurement is that it is the distance from the face of a locked bolt to a shoulder in the chamber that arrests the forward movement of a cartridge.

Need some reloading help? The Lyman 50th edition reloading handbook has you covered!

WHAT HAPPENS

A lot of things happen in very rapid succession when a shooter pulls the trigger. The strike of the primer upsets the shock-sensitive priming mix. The priming mix detonates and shoots a small flame through the flash hole into the primer pocket, which ignites the gunpowder. The result of that explosion is a gas that rapidly expands, stretching the ductile brass case. While the solid rear area around the primer pocket remains close to the original size, the thin case wall in the front is pressed against the chamber wall. With the solid rear remaining close to its original dimensions, which is just slightly smaller than the chamber. The gas pressure forces it back against the bolt face, while the still expanding gas creates a thrust that pushes the bullet out of the case. Shewww! That's a whole lot easier to visualize than explain, and a whole heck of a lot quicker! But I think you get the picture, or I hope so anyway.

The Lyman .224 Valkyire headspace gauge. The perfect tool for ensuring you have the right amount of headspace.

WHY THIS IS IMPORTANT

SAFETY and ACCURACY! Having too much headspace is bad, and having too little headspace is bad. The tolerance measurement for the best accuracy should be zero. Ideally, all of the space behind the case head should be eliminated. When the case head is just touching the bolt face, the cartridge is well aligned in the chamber. This also allows the case to stay firmly in place under the impact of the firing pin striking the primer. Having too much headspace could lead to case ruptures. A case rupture could lead to catastrophic failure and cause serious injuries. It could also result in unseated primers after you fire, case separations, split case shoulders, a blown case, a light primer strike, or simply a failure to fire. Having too little headspace or an excessively tight fit can prevent the firearm from going into full battery. Not being able to set in battery will result in either deformation of the cartridge case, or a failure to fire. Even if the round can be chambered with a little force, it could cause functioning and feeding issues.

Making your own builds? It's always important to be as accurate as possible. Make sure you check your headspace if you're building from a parts kit like this Romanian PM-90 AK Parts Kit. Or check any of the guns you own for the best performance possible.

THE SKINNY OF IT ALL

I could go truly in-depth with the science of headspace, and it literally comes down to the "inths" in physical measurements. What is important to know is that to ensure an efficient ignition, the full force of the firing pin strike needs to be delivered to the priming cup. You can adjust headspace with the correct tools. If you are an advanced reloader
, or even just a beginner, Classic Firearms has everything that you need, from manuals, complete kits, or new dies. Check out our inventory and unbeatable low prices for your reloading needs. Shop All Reloading Supplies
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