Carbine vs Mid Length Gas Systems – 2022 Explanation

Sometimes selecting between two similar options is challenging. A small difference could impact your level of satisfaction with the product.

When you compare two or more weapon components, it's usually vastly different. In terms of carbine versus mid length, this isn't the case. These are two phenomenally similar uppers that only have one major difference. 

This article delves into each of these products' details and lists the advantages, disadvantages, and additional facts about each. It provides a comparison in the form of a table.

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TL;DR: Carbine vs Mid Length

Carbine Length

Mid Length



More Compact

Lighter Weight

Can be harder on components

It’s easy to accessorize

Extra length offers shooter comfort and versatility of shooting techniques

Offers slightly less recoil



Its appearance can seem disproportionate

Not conducive to large accessories or bayonets


It’s not ideal for military use

Best For

Best For

Military and tactile usage

Civilian use on small to medium weapons

What Is a Gas System, & What Is Its Purpose?

A gas system replaces the firearm's need for a manual bolt. The direct impingement system and bolt carrier group interact directly. This automatically cycles the bolt, meaning that each time you squeeze the trigger, the bolt cycles back and forth. Ammunition then discharges in a semi-automatic manner.

Ordinarily, when the hammer or striker hits the primer, it ignites the powder in the cartridge, which in turn causes heat, pressure, and hot gas. This gas expels the bullet, and the excess gas follows it out the barrel. 

A gas system harnesses the energy from the excess gases and utilizes it productively to cycle the rounds. You can do this by installing a gas block that traps a portion of the extra gas and transports it to a tube situated above the barrel.

The gas is then sent back up to the receiver, where it flows into a key. This key is screwed above the bolt carrier group. Here it expands and forces it back into the buffer tube.

Simultaneously, the old shell casing is removed by an extractor. This allows space for the new round. At this point, the components inside the buffer tube compress before quickly expanding to shoot the bolt-carrier group back into the upper receiver.

As the bolt carrier group travels forward, it extracts a new cartridge and chambers it. The weapon is now ready to fire again. On firearms that don't use gas, you would have to manually perform some of these actions.

There are several types of gas blocks. The most common is a low-profile gas block that works well with free-floating handguards. You also get front sight post gas blocks and adjustable gas blocks. 

There are different types of gas systems, such as direct impingement and the gas piston. The primary purpose of a gas system is, therefore, to efficiently utilize the excess gas to cycle rounds automatically. 

Relevant Characteristics Between Carbine and Mid Length

Carbine Length



carbine length gas system

Courtesy of 03DesignGroup

mid length gas system

Courtesy of 03DesignGroup

Gas Port Pressure

26,000 PSI

21, 000 PSI

Barrel Length

10 to 20 inches

14 to 18 inches

Dwell Time

3 to 13 inches

5 to 9 inches

Port Distance

7 Inches

9 inches





Slightly Higher

Slightly Lower

Similarities and Differences

Below, we discuss some of the common features as well as contrasting aspects of these two upper components.

Carbine and Mid-Length Gas System Differences

If you take the two products and place them side by side, the most apparent difference, appearance-wise, is the size. The carbine is compact and approximately 2 inches shorter than the mid length (excluding barrel length which can vary). The gas system is also not the same. 

The entire carbine system is smaller, so the vent hole is closer to the receiver than on a mid-length system. This has a direct impact on the way gas cycles within the weapon.

For example, if the bullet has already traveled past the vent hole but remains in the barrel for longer, more gas will enter the vent hole. If the hole is closer to the barrel, a reduced amount of gas will enter the tube.

Carbine systems have more gas entering the tube in comparison to mid-length systems. These are essential aspects to consider when making your decision because if you select an option that's too short, there'll be too much gas going into the receiver.

This can result in excess recoil. It will also cause your weapon to wear easily, and your gun might get dirty easier. If the system you select is too long, you may have trouble getting adequate gas from flowing back.

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Having insufficient gas means that you won't have enough force, and your bolt carrier group might not be able to extract cartridges to chamber the next round. The system you select should be paired with an appropriate weapon.

You need to consider buffer weight, the type of gas block, and ammunition type as well. 

Carbine and Mid-Length Gas System Similarities

Both of these options are gas-operated. They use the excess gas from a fired cartridge to power the automated system that would otherwise have to be done manually. This system uses the energy from these gasses to perform two functions.

The first function is to remove the old cartridge casing after firing a bullet, and the second is to retrieve a new cartridge from the magazine and place it in the chamber so that it's ready to be discharged. This basic functionality is the same on all gas systems.

You can also find common barrel sizes among the two. Both mid-length and carbine systems can fit similar muzzle types as well.

Advantages of Carbine Length Gas Systems

The carbine gas system is more compact than the other options available, and as a result, it's also slightly lighter. Small differences in weight can have a significant impact when walking long distances. 

This makes the carbine option better in adverse conditions and is one reason it's ideal for military use. In terms of ammunition, this gas system is also the least sensitive, even if it’s offset with slightly more recoil. 

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The carbine is the ideal product for barrels that are short or medium length. Many consider the dwell time of the carbine to be an advantage over the mid length. This is because an inadequate amount can result in short stroking.

The carbine system can still perform optimally in dirty and dusty conditions such as war zones. This is why carbine is considered a military-type product and is created similarly to the M14.

Advantages of Mid-Length Gas Systems

Gun enthusiasts often say that if you're working with a 16-inch barrel on a carbine that you might as well opt for a mid-length system. There are several notable benefits of this option. Many claims that it runs cooler and smoother as well.

Gas pressure is complex. Having too much of it may cause problems, but too little causes issues, too. The mid length offers an ideal medium between these extremes. 

When the combustion gasses travel far from the chamber, they become cooler and thus have less pressure. As a result, the bolt velocity is reduced.

In this circumstance, there's still enough energy for the system to operate optimally without causing issues such as excessive bolt bounds, jams, or slippage. It also offers the shooter much less recoil.

The gas port pressure in a mid-length system is a healthier baseline than a carbine. The lower pressure allows for a larger gas port, and in turn, the margin of error is much lower. 

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Another benefit of this product is that you have more length on the handguard. Typically, a mid length gives you two extra inches if your AR handguards don't extend beyond the block. The extra space allows more comfort and versatility in terms of shooting techniques.

The extra length also helps when you want to install accessories such as lasers and lights. Aside from these accessories, some gun enthusiasts want to mount bayonets on their weapons. It's a lot easier to do this on a mid-length system.

The mid length is also more attractive looking with comfortable proportions. It's a favorite for civilian shooters.

What About Rifle-Length Gas Systems?

A rifle-length gas system is the longest of these products, and the gas tubes measure approximately 13 inches. These systems are ideally suited for barrels longer than 20 inches or marksman-type AR15 firearms.

The location of the gas port on these weapons accommodates a bayonet. As a result of this, a particular lug is built into the gas block. Rifle-length gas systems are comfortable to shoot, and the bolt carrier group moves slightly slower in this model.

It offers shooters a smooth action and fantastic reliability. The handguards of these range between 11.5 to 12 inches in length and offer the least recoil. 

A long-range AR build featuring a rifle-length gas system. Photo credit:

Bottom Line

Each gas system serves a purpose and is suited to different applications. The carbine is rugged, compact, and practical but has a heavier recoil than the other options. The mid length is smoother and aesthetically pleasing and designed specifically for the civilian market.

Both options are reliable and have the same functionality. If you're looking for a gritty weapon that can perform well in harsh environments, your best bet is a carbine. On the other hand, if you want a smooth shooting weapon with minimal recoil, you're better off with a mid-length system.

People Also Ask

When it comes to gas systems, many questions arise. This section highlights some of the most common questions regarding this topic. 

Why Does Gas System Length Matter?

There are several reasons that the length of the gas system you choose is important. It should increase as your barrel length increases. On a longer barrel, you'll need a system with a more extended dwell.

Having too much or too little can cause problems such as inefficient cycling and jams. Pistol systems are best for barrels smaller than 10 inches, carbines for barrels 10 to 18 inches, mid lengths for 14 to 20 inches, and rifle systems are best for barrels longer than 20 inches.

Can You Put a Mid-Length Handguard on a Carbine?

It's advisable to fit the correct handguard length to each system. If you use a low-profile gas block, it's possible to fit a mid-length handguard on a carbine for a longer gripping area or appearance purposes.

Can I Use a Carbine Buffer in a Mid Length?

It will probably work, but it's best to pair a mid length with the buffer designed for it.


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