- M4 rifles are made to military specs
- AR-15s are made to a broader civilian spec
- The M4 is select-fire while most AR-15s are semi-auto-only
When it comes to firearms, there is no mistaking the similarities between an M4 and an AR-15, which leads many to ask: what makes these two guns different?
Depending on which AR-15 is used for comparison, there are many differences between an M4 and the broader AR-15 family. This means it’s time to go over what's involved.
What is the Difference Between an AR-15 and an M4?
The difference between an AR-15 and an M4 comes down to the rifle parts and their specifications. Each has its own dimensions, requirements, and purposes in manufacturing. This can make them visually similar but functionally unique.
Let’s start with the least changing gun: The M4 Carbine.
M4 Specifications
The M4 was introduced officially in 1994 as an issued rifle. It featured a 14.5-inch government profile barrel with an A2 flash hider, a collapsible stock, a brass deflector, a bayonet lug, and an A2 front sight.
Some very early models had a fixed carry handle, but this was quickly replaced with a Picatinny flat-top rail. All this would combine into a short, maneuverable sibling of the M16 line of rifles as US doctrine adjusted to newer experiences in Mogadishu.
Key Differences: M4 vs. AR-15
The largest unique difference between the M4 and the AR-15 is the use of a burst fire trigger pack. This would allow the rifle to fire in semi-auto or 3-round burst modes.
M4A1
Shortly after its adoption, the M4 would be improved into the M4A1. The early differences would be the use of a SOCOM profile barrel, which enabled higher fire rates and under-slung grenade launches, before switching back to the standard government profile.
The other major difference would be the use of a fully automatic trigger pack replacing the 3-round burst function.
Role in the Military
The M4A1 was originally designed and issued to special forces units in the mid-1990s and early 2000s, but it would slowly be integrated into the regular infantry. It remains the most commonly issued rifle for the US into the 2020s as the M7 entered service in 2024.
| Specification | M4 Parts |
| Barrel | 14.5 inches |
| Trigger Pack | Select Fire: Burst and Full Auto packs |
| Receiver Styles | A2 Carry Handle and Flat Top |
AR-15 Specifications
Compared to its military cousins, the civilian AR-15 is the wild west of configurations. While both the M4 and the AR-15 were influenced by the SOPMOD program for accessories, the AR-15 has a wider field of accepted parts than the M4.
Barrel Options
An AR-15 barrel can range from below 10.5 inches all the way to 22 inches, with the most common offerings being 10.5 to 20 inches in length. They can have every kind of flash hider and compensator for 5.56/223, and they have multiple gas systems available.
Trigger Pack
The trigger pack is semi-auto only for non-NFA rifles, and the gas block can feature A2 versions or a low-profile option, making it one of the most customizable rifle platforms on the market.
| Specification | AR-15 Parts |
| Barrel | 10.5 to 20 inches |
| Trigger Pack | Semi-auto only |
| Receiver Styles | Flat Top, Integrated Rear Sights, Carry Handle |
Why Are the M4 and AR-15 Different?
The M4 vs AR-15 question does not make any sense if you don’t know the history of the platform's design, especially when some AR-15s can be made to look extremely similar to an M4 (often called an M-Forgery).
Historical Context
So what is the difference between an AR-15 and an M4? The reason they are different is the market they are designed for. Originally, the term AR-15 was a registered trademark used by Armalite, which then sold the rights to Colt when the Military’s contracts required greater manufacturing capacity for the early M16.
Rights and Reproductions
Colt eventually lost the rights to the copyright, which led to the rest of the civilian sector making copies of the designs.
Quality Variations
These copies did not follow Armalite or Colt’s technical package for the AR-15, leading to varying build and parts quality. So you can have rifles that are visually similar but of different qualities.
Does It Matter That M4s and AR-15’s Are So Similar?
At the end of the day, it really does not matter that the AR-15 and the M4 are similar designs. The M4 is made to military specifications for military use levels. The AR-15 is made to whatever specifications the manufacturer chooses.
Exploring AR-15 Tiers
This creates the “tiers” AR-15 customers are used to looking through. Some AR-15s are extremely affordable but not built for heavy use, while others are expensive and built to withstand years of heavy use.
Customization vs. Military Specifications
The AR-15 is made for your wants and needs, while the M4 is made to the Government's parameters. If you’re looking for some AR-15 parts, check out our in-stock offerings or contact us to speak with our resident experts.
Frequently Asked Questions
Are AR-15s Legal?
Yes, AR-15s are legal in most states and at the Federal level. However, some states like California heavily restrict AR-15 features, while locations like Illinois have banned new purchases of the design.
Is My AR-15 Military Grade?
More than likely, no. Most civilian AR-15s are not made to the same specifications as military M16s or M4s. This is predominantly connected to a lack of select fire capabilities for modern AR-15s without the appropriate NFA paperwork.
What Does AR Stand For?
The term AR in AR-15 stands for Armalite Rifle or Armalite Research, depending on the historical source. This is because the AR-15 was developed by Armalite, and the design was assigned the number 15.
Can I Buy an AR-15 Online?
Yes. You can purchase an AR-15 online, and it will be shipped to your local FFL holder.
Do I Need a Tax Stamp For An AR-15?
For most AR-15s, you do not need a tax stamp. However, some variants that do meet the requirements for being an NFA item will need a tax stamp in order to be legally owned.
What Caliber is the AR-15?
Civilian AR-15s are chambered in 5.56x45 NATO or .223 Remington. Some variants are chambered in other calibers, but their designations will reflect which caliber they are. Example: AR-308s are chambered in .308, and AR-9s are chambered in 9mm.
Is the AR-15 Full Auto?
No, modern AR-15s are not normally made with a full-auto trigger pack. There are legal ways to upgrade the rifle to full auto, but those require an NFA tax stamp. Additionally, the early versions of the AR-15 by Armalite were full-auto designs, but this function was removed for civilian sales.
Does the AR-15 Use Armor-Piercing bullets?
While there is 5.56 armor-piercing ammunition, most ammunition on the civilian market does not meet the legal definition of armor-piercing.