Bolt Face: What Does it Mean?

What Does Bolt Face Mean?

When we are online there are a lot of terms used in the firearms community that everyone expects you to know. “Bolt face” is one of those terms but very often it is thrown out there without any explanation as to what it is.

Today we are going to look at the definition of bolt face and why it is important.

Standard Definition

The bolt face is the front area of the bolt that makes contact with the base of the cartridge. This area usually holds the firing pin and extractor(s) on centerfire rifles. This is the area that also pushes the cartridge into the chamber.

This is relatively simple to understand until you start dealing with alternative names for the bolt face. They are all the same thing, but they are called something different especially in older references.

These alternate names are the breech face, the breech block face, and the breech bolt face according to the Small Arms & Ammunition Manufacturing Institute (SAAMI) glossary of terms.

Why Is The Bolt Face Important?

There are a couple of reasons as to why the bolt face is important. These are generally very utilitarian in nature and just make sense when you look at them from the outside, and they all come down to ammunition.

1. Ammunition fits in the chamber

The size of the bolt face has to accept the cartridge base it was designed for. This is governed by two major organizations which are SAAMI and the C.I.P. (English translation: Permanent International Commission for the Proof of Small Arms). These are essentially the US and non-US sources of proof testing.

Since they cater to different spheres of influence SAAMI and the C.I.P. do not always agree on the minimum and maximum dimensions of cartridges, chambers, and bolt faces. Some manufacturers will work within these parameters in order to allow for the widest variations in ammunition.

This is because mass ammunition manufacture will always have several thousandths of a degree differences between individual items. Your bolt face has to work with most if not all of these in order to be reliable.

The minor variations between ammunition manufacturers and ammunition lots need to be accounted for when making a bolt. Some bolt manufacturers will have tolerances as close to spec as possible on their bolts in order to ensure the proper feed and function in the gun.

A perfect example of this is the Defiance Classic Action which has a bolt face of 0.480 inches on their Medium Short Action option. This is the recommended bolt face for .308 Winchester since .308 has a case range of 0.4630 to 0.4730 inches (per Ultimate Reloader’s research).

As long as the ammunition’s case falls at or between those two numbers, the Classic Action will work. Which brings us to the second reason why bolt face matters.

2. Reloading Dimensions

When you are focused on accuracy, long distance shooting, and other bolt action rifle tasks, reloading becomes a very viable option for your ammunition. Ammunition is the major weak point for most precision rifles.

This is why many precision rifle shooters will start reloading or manufacturing their own ammunition. The reason for this is better quality control. If you are only making 100 or less rounds at a time, you have the ability to check the dimensions of every round there.

Knowing your rifle’s bolt face will allow you to determine if your ammunition will work in your rifle, even when it isn’t as in spec as it could be. Using the same brass over and over again  will eventually fatigue it and the case base may wear down over time resulting in that brass being retired or melted down.

Keep in mind most of your brass’s life will come down to the case neck, not the case base. However, making sure the dimensions of your ammunition is within the safety parameters is the best way to keep everything where it should be and not catastrophically failing.

Conclusion

In the grand scheme of your rifle, your bolt face only has to match your ammunition enough to cycle it safely and reliably. Some individuals believe the bolt face will impact accuracy and include it on their list of parts to accurize, but there is little evidence to support this.

If you are looking to upgrade your rifle’s bolt for better consistency we have a number of offerings from Defiance, Impact, and Stiller that may fit your needs.