Why the X in XM Ammo?

XM Ammo
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Why the X in XM Ammo?

The gun world can be confusing to the uninitiated, especially with all of the information and designations for each individual component.

Ammunition is no different. There are so many numbers and letters on the packaging that it can be difficult to know what’s what — and that’s without getting into grain and calibers.

In most instances, these designators aren’t arbitrary. They typically have specific meanings that help you select the right products.

In fact, that tiny box of ammunition contains a whole world of information if you know what you’re looking at.

While every letter or number isn't necessarily a big deal, they all tell you something. 

What is the X in XM Ammo?

The short answer is that the X is a separate designator representing that ammunition is for civilian rather than military use.

The slightly longer answer is that this ammunition is made in a similar manner to that of the military ammunition, to fit and be fired from the similar styles of guns, but lacking a specific requirement for the military designation or was never intended to be sent to the military.  

Who Uses X Ammo?

It’s entirely possible that you’ll see an X on an assortment of rounds from different manufacturers.

However, the primary company to use this designation is Federal Ammunition. Federal supplies a large amount of military ammunition, so it developed the X for its various brands as a way to identify certain ammo more readily.

That said, there are other manufacturers who might place an X in front of their round designations for different reasons.

Some might use it to represent a name, to indicate some kind of performance or even as a sales pitch, such as "extreme".

On the other hand, others might be attempting to copy what Federal is doing. Whatever the reason, there could be other ammo out there with an X that has nothing to do with the original intended use.

Keep that in mind and be thorough in reading the boxes that you buy.

Why is XM Ammo Necessary?

There are actually many potential reasons for the letter designators on the ammunition, not the least of which is distinguishing between military and civilian ammo.

This is the case with the Federal-branded XM ammunition, which is specifically for civilian use. Like most things involving the military, there are strict rules in place.

So, in order to mitigate this, ammunition not designated specifically to be used by the United States military gets the addition of the X to it.

Simply put: M is for military use and XM is not. 

In addition to describing the ammunition, these letters can help with regulations and with the manufacturer producing the ammunition to ensure it's sending the right ammo to the right places.

As a manufacturer, you are held to very specific guidelines for the production of ammunition as well as how you deliver it.

Manufacturers absolutely do not want even a small amount to go to the wrong place.

Something like that could cause a company to lose a government contract or face even more serious consequences.


For the record, it’s worth clarifying here that just because something “doesn’t meet the standards” for military specifications doesn’t mean it’s an inferior product.

Not all of the standards for mil-spec ammunition revolve around its ability to fire or perform.

Military standards involve many details and sometimes vary based on the intended military use or even how they want the ammunition packaged and delivered.

All of these things combine to make it mil-spec, and so the difference on what you receive marked XM could really be something small.


One of the biggest differences between civilian and military ammunition is pressure.

Most military cartridges are designed with a higher-pressure load, and that could be catastrophic for certain civilian firearms.

This is true for handguns too; most civilian 9mm pistols aren’t designed to handle the chamber pressure of a 9mm NATO round.

Granted, there are plenty of modern firearms that are capable of withstanding this pressure difference, but in the military, every firearm was made for this specific purpose.

Twist Rate

Another factor is the twist ratio of the rifle barrel.

Certain rounds perform better at specific twist ratios, and military rifles share a designated twist rate based on what type they are.

The American M4, for example, utilizes a 1:7 twist rate. What this means is that the grooves in the barrel are designed so the round completes one full rotation every 7 inches.

With civilian rifles, you can find various twist rates with the most common being 1:8 or 1:9.

This difference might not seem like much, but it matters for a variety of reasons — not the least of which is accuracy.

Since some rounds perform better with certain twist rates, it’s important for the military to get the right rounds for their rifles. 


The differing designation can help for civilians as well because there are some instances where being non mil-spec could benefit you as a civilian shooter.

Military specifications are extremely rigid, meaning the government requires that the rounds be made of exactly what they say and how they say.

With civilian ammo, even those otherwise meeting the same dimensions and caliber requirements, there is room for experimentation.

Manufacturers are able to try out different round designs, case materials and even change the makeup of the actual round itself.

Variety might be the spice of life, but not in the military. Everything must be exactly the same and completely uniform.

There is absolutely no room for deviation. It doesn’t matter how good something is or even if it offers improvements. Unless the military specifically asked for it, they don’t want it.

As a civilian shooter, you get the benefit of better and more innovative rounds that military shooters may not enjoy.

Bottom Line

The bottom line is that while there is a need for the X in XM ammo, it really doesn’t have that much meaning to you as a consumer or firearms enthusiast.

It’s good information to know and have, because more information is always a good thing when you're shooting or caring for guns.

But, really, there is information on the ammo box that's a lot more important than the X.

Things like the grain of the round or whether or not it’s ball ammunition or hollow point are examples.  

There are many letters and numbers that go along with most things in the gun community.

From the firearms themselves to the ammunition and even the accessories, designations are common.  Knowing what they are is important, but there’s no need to worry if you see something you don’t know.

The other information you see can help clue you in and, if necessary, you can always ask. Or you can always visit your favorite ammunition website’s blog section.

After all, that’s what we’re here for.

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