There are several ways to measure the length of an AR 15. Some prefer to classify length by the gas system. Others use the barrel length. Still others prefer to classify length by AR 15 upper assembly length or overall rifle length. We will discuss all the different ways to measure an AR 15 and go over the benefits and drawbacks to each length.
There is no best length for every circumstance, that’s why there are so many different lengths. Depending on what you need to accomplish, there is a best length for each task. We are going to look at the most common measurements and what they are best suited for.
We are only going to go over different lengths we will not be going over caliber, which also affects the performance of the weapon.
How to Measure an AR 15 Length
One of the first things to consider when looking at the length of an AR 15 Upper is to decide if you have a rifle or pistol. Because there are different components that qualify a weapon as a pistol or rifle. One of the first things to consider, is the stock. The stock is only one of the features that define a weapon as a pistol or rifle. So, if you have what might otherwise be categorized as a pistol, but you install a rifle stock onto it, it would be then recategorized as a short-barreled rifle.
Once you know what type of weapon you are measuring, it is a good idea to understand why you are wanting to measure it. If it is to be sure it is going to fit into a safe, or carry bag, you will want to know the overall length. If it is for legal reasons, you will most likely want someone certified to look at it for you.
That being said, it is not too difficult to measure the components of your AR 15 if you are curious about the measurements. Below we will take a closer look at how to identify and measure each of the different ways to measure your AR 15.
Gas System Length Explained
The Gas system on an AR 15 is one of the easiest ways to identify. The different lengths are enough different that they are generally identifiable just by sight. The gas system is located on the top of the barrel, typically under the handguard. It is what send gas from the expended round back to the BCG allowing the spend round to be expelled and the new round loaded.
If the gas system is too short, it will send too much gas back to the receiver. This creates greater recoil that wears parts out faster. Shorter gas systems must be accounted for with adjustable gas blocks and/or heavier buffers.
If the gas system is too long, it will not send enough gas back to allow the BCG to operate properly. This means the rifle may jam without the proper force applied to the BCG to extract and chamber the rounds.
There are four standard gas system lengths.
The shortest is pistol length. The average length for a pistol length gas system is 4.5 inches. This provides for a very fast and heavy cycle. Creating increased recoil, so rapid follow-up shots tend to be less accurate. It may also require a muzzle device with heavy upward gas deflection to decrease muzzle rise. This is the length of gas system for very short barrels such as 7.5-inch barrels.
A carbine length gas system is the most common gas system, and the gas tube is about 7.5 inches long. This system works best with barrels between 10-18 inches long. For a barrel that is 10 inches long the carbine length is a good choice eve though you can still get a 10 inch barrel with a pistol length gas system.
A mid-length gas system is a bit longer than a carbine length and measures at about 9.5 inches. Rifle with longer barrels in the 14–20-inch length performs better with mid-length gas systems.
A rifle length gas system is the longest system at about 13 inches long. A rifle length gas system is best for rifles with 20 inch or longer barrels. This includes barrels of 24 inches as well. These are used primarily for marksman who want to shoot longer distances.
Barrel Length Explained
The next common way to measure the length of an AR 15 is to use the barrel length. Read this to learn how to exactly measure barrel length. But overall, you probably know the general length of your barrel. This is a good way to describe to yourself or other people how long your AR 15 is. In fact, if you say, you have a 16-inch AR 15, most everyone understands you have a 16-inch barreled AR 15.
If you have an AR 15 with any barrel shorter than 16 inches, you run the risk of it being defined as a pistol or AOW. So, the rule of thumb, is to be sure you have a 16” barrel if you want a rifle. Barrels commonly are sold commercially from 7.5 inches to 20 inches, with 16 inch being the most common.
The longer the barrel, the more accurate at farther distances it can possibly fire. I say possibly fire because it still depends on other factors, such as what rifling, caliber, and sights are being used. Also, what is the altitude and weather conditions when using.
Do not forget to check the location of the gas port on the barrel when measuring it for length. Especially if you are tuning your weapon. As barrel length increases it will often require a longer gas system.
Very often an AR-15 platform weapon can be customized to meet a great many length requirements. That is one of many of the wide range of features of an AR 15.
Upper Assembly Length Explained
Another way to measure the length of your AR 15 is to measure the overall upper assembly. The reason for measuring this way might be because you are separating the upper and lower sections for easier transporting and want to be sure to buy a proper carry bag, chest, or box for transporting. The way to measure this way would be to simply remove the upper assembly from the lower assembly and measure the upper from the muzzle device to the rear of the upper receiver or charging handle if left in. This will typically be the longest section of the rifle when separated.
This measurement can vary greatly from upper to upper. So, if you are curious, use a tape measurer, or yard stick to get the overall length of your upper receiver.
Overall AR 15 Length Explained
The overall length of your AR 15 is easy to measure. If you have a collapsible stock, put it in the shortest position. Then, measure from the stock to the muzzle device. This will give you the overall length of your AR 15. This measurement may be useful if you are going to use a mount. It will also be important if you are shopping for gun safes or carry bags.
There may be times where as little as ½ an inch may make all the difference between fitting or not fitting. The easiest way to change the overall length of your rifle is to change the stock. There are a multitude of different stocks to choose from. Stocks come in oversized, extended, standard, and compact. So, determine what you need and shop accordingly.
Shopping for AR 15 Parts
If you are clear on the length of rifle or pistol you want for your next AR 15 build and want the best prices and selection on AR 15 Parts, shop now at Black Rifle Depot. With live inventory and five star customer service, you can shop happy. With a wide variety of options to choose from take your time exploring the AR 15 Products including bolt carrier groups, free float handguards, stocks, barrels, and grips.