The AR-15 can be assembled using a few different gas tube lengths depending on the barrel length and where the gas port is located on the barrel. But what gas tube length do you use for an AR-15?
The gas tube used for an AR-15 with a barrel less than 10″ is a pistol length gas tube, for a 10-18″ barrel it’s a carbine length gas tube, for a 14-20″ barrel it’s a mid-length gas tube, and for 20″ or longer barrels it’s a rifle length gas tube.
That’s a good guide to use in general, but there’s more to picking a gas system length. Also, the actual measurements of the gas tube can vary depending on manufacturer.
AR Gas Tube Lengths
There are 5 different gas tube lengths used on the average AR-15 with each length having a range of measurements. Pistol, carbine, mid, intermediate, and rifle length gas systems can be used on a number of different barrel lengths.
For example, a 14 inch barrel can be sold with a carbine gas system or a mid-length gas system. It all depends on where the gas port is drilled in the barrel. That will determine which gas tube length you need. So look at the specs of the barrel you’re buying.
Here’s a reference chart showing the actual measurements of the different gas tube lengths:
| Gas Tube Length | Measurement (inches) |
|---|---|
| Pistol Length | 6.625 – 6.75 |
| Carbine Length | 9.25 – 9.8 |
| Mid-Length | 11.25 – 11.75 |
| Intermediate | ~13.25 |
| Rifle Length | 15.125 |
Don’t confuse gas tube length with the port length on the barrel. The gas tube will usually be a couple inches longer than the port length since the gas tube needs to stick into the upper receiver a little bit.
What’s The Best Gas Tube Length For An AR-15
The best gas tube length for an AR-15 is a 9.75″ carbine length gas tube on a 14.5″ carbine barrel like the M4 used by the US Army. However when using a 16″ barrel, the mid-length gas tube will allow the firearm to function better than a carbine length.
The best gas tube length is somewhat a matter of opinion, but also it depends on which barrel length you want to use. I wouldn’t pick a barrel length based on which gas system I wanted. I would pick the gas system based off the barrel I need for a certain application.
A general rule of thumb is that the closer a barrel length is to the middle of it’s suggested range, the better it should function.
Here’s a reference chart showing the optimal barrel length for the different gas tube lengths:
| Gas Tube Length | Barrel Range | Optimal Barrel |
|---|---|---|
| Pistol Length | 10″ or Under | 8″ |
| Carbine Length | 10-18″ | 14.5″ |
| Mid-Length | 14-20″ | 16″ |
| Rifle Length | 20″ or Longer | 20″ |
How Long Is A Pistol Length Gas Tube?
A pistol length gas tube measures between 6.625 – 6.75 inches depending on manufacturer. The majority of pistol length gas tubes are 6.75 inches long and are designed to be used with a standard pistol length barrel on an AR style rifle.
Pistol length gas tubes are designed for barrels 10 inches or less that are set up for pistol length gas systems. Meaning the gas port on the barrel is drilled at the correct spot to allow the proper fitting of pistol length gas tubes.
What Is The Port Distance On a Pistol Length Barrel?
The port distance on a pistol length barrel is normally around 4 inches from the rear of the barrel. The gas tube needs to make up the port length plus an additional couple inches to extend into the gas key on the bolt carrier in the upper receiver.
How Long Is A Carbine Length Gas Tube?
A carbine length gas tube measures between 9.25 – 9.8 inches depending on manufacturer. The majority of carbine length gas tubes are 9.5 inches long and are designed to be used with a standard carbine length barrel on an AR style rifle.
Carbine length gas tubes are designed for barrels 10-18 inches that are set up for carbine length gas systems. Meaning the gas port on the barrel is drilled at the correct spot to allow the proper fitting of carbine length gas tubes.
What Is The Port Distance On a Carbine Length Barrel?
The port distance on a carbine length barrel is normally around 7 inches from the rear of the barrel. The gas tube needs to make up the port length plus an additional couple inches to extend into the gas key on the bolt carrier in the upper receiver.
How Long Is A Mid Length Gas Tube?
A mid length gas tube measures between 11.25 – 11.75 inches depending on manufacturer. The majority of mid length gas tubes are 11.5 inches long and are designed to be used with a standard mid length barrel on an AR style rifle.
Mid length gas tubes are designed for barrels 14-20 inches that are set up for mid length gas systems. Meaning the gas port on the barrel is drilled at the correct spot to allow the proper fitting of mid length gas tubes.
What Is The Port Distance On a Mid Length Barrel?
The port distance on a mid length barrel is normally around 9 inches from the rear of the barrel. The gas tube needs to make up the port length plus an additional couple inches to extend into the gas key on the bolt carrier in the upper receiver.
How Long Is A Rifle Length Gas Tube?
A rifle length gas tube measures around 15.125 inches depending on manufacturer. The majority of rifle length gas tubes are 15.125 inches long and are designed to be used with a standard rifle length barrel on an AR style rifle.
Rifle length gas tubes are designed for barrels 20 inches or longer that are set up for rifle length gas systems. Meaning the gas port on the barrel is drilled at the correct spot to allow the proper fitting of rifle length gas tubes.
What Is The Port Distance On a Rifle Length Barrel?
The port distance on a rifle length barrel is normally around 12 inches from the rear of the barrel. The gas tube needs to make up the port length plus an additional couple inches to extend into the gas key on the bolt carrier in the upper receiver.
AR Gas Tube Diameter
The average AR gas tube inner diameter is 0.120 inches and the average outer diameter is 0.180 inches giving an average thickness of 0.060 inches. However, better quality stainless steel, thicker walled tubes, and seamless vs welded-seam tubes all have slight variations in diameter.
Gas Tube Length For a 10.5″ Barrel
For a 10.5″ barrel a carbine length gas tube measuring between 9.25 – 9.8 inches should be used. However, the gas tube needs to be selected based off the port distance on the barrel measured from the chamber to the gas port on the barrel.
They do make 10.5 inch barrels setup for either pistol or carbine length gas systems. A barrel designed for a carbine length gas system will have a port distance of 7 inches. A barrel designed for a pistol length gas system will have a port length of 4 inches.
Gas Tube Length For a 16″ Barrel
For a 16″ barrel a mid length gas tube measuring between 11.25 – 11.75 inches should be used. However, the gas tube needs to be selected based off the port distance on the barrel measured from the chamber to the gas port on the barrel.
They do make 16 inch barrels setup for either carbine or mid length gas systems. A barrel designed for a carbine length gas system will have a port distance of 7 inches. A barrel designed for a mid length gas system will have a port distance of 9 inches.
Gas Tube Length For an 11.5″ Barrel
For a 11.5″ barrel a carbine length gas tube measuring between 9.25 – 9.8 inches should be used. However, the gas tube needs to be selected based off the port distance on the barrel measured from the chamber to the gas port on the barrel.
A barrel designed for a carbine length gas system will have a port distance of 7 inches.
Gas Tube Length For a 12.5″ Barrel
For a 12.5″ barrel a carbine length gas tube measuring between 9.25 – 9.8 inches should be used. However, the gas tube needs to be selected based off the port distance on the barrel measured from the chamber to the gas port on the barrel.
A barrel designed for a carbine length gas system will have a port distance of 7 inches.
Gas Tube Length For a 14.5″ Barrel
For a 14.5″ barrel a carbine length gas tube measuring between 9.25 – 9.8 inches should be used. However, the gas tube needs to be selected based off the port distance on the barrel measured from the chamber to the gas port on the barrel.
They do make 14.5 inch barrels setup for either carbine or mid length gas systems. A barrel designed for a carbine length gas system will have a port distance of 7 inches. A barrel designed for a mid length gas system will have a port distance of 9 inches.
Gas Tube Length For a 20″ Barrel
For a 20″ barrel a rifle length gas tube measuring 15.125 inches should be used. However, the gas tube needs to be selected based off the port distance on the barrel measured from the chamber to the gas port on the barrel.
A barrel designed for a rifle length gas system will have a port distance of 12 inches.
Gas Tube Length For an 18″ Barrel
For an 18″ barrel a mid length gas tube measuring between 11.25 – 11.75 inches should be used. However, the gas tube needs to be selected based off the port distance on the barrel measured from the chamber to the gas port on the barrel.
They do make 18 inch barrels setup for either mid length or rifle length gas systems. A barrel designed for a mid length gas system will have a port distance of 9 inches. A barrel designed for a rifle length gas system will have a port distance of 12 inches.