AR-15 Gas System Identification Guide

By CTD Blogger published on in General

There are four main lengths of AR-15 gas systems in use today: Pistol, Carbine, Mid and Rifle. Each one of these gas systems require different length gas tubes and handguards, so it is important to know which one you have before ordering parts for your AR-15.

If you don’t know what size rifle you have, it is fairly easy to determine by simply measuring the length of your handguards or gas tube.


Three samples of handguard lengths in gunmetal gray

A side by side comparison of Carbine, Mid-Length, and Rifle Length handguards.

The pistol-length gas system is used almost exclusively on AR-15 pistols or AR-15 rifles with very short barrels, usually 10 inches long or less.

These systems generally have a gas tube of approximately 4.5 inches. The handguards or free-float tubes for these systems are generally between 3 to 4 inches in length.

Some people are now installing low-profile gas blocks and carbine length free-float handguards so that they can have a longer and more comfortable forearm grip area.


The carbine-length gas system, combined with barrel lengths from approximately 10 to 18 inches, is perhaps one of the most common setups across all types of AR-15 rifles.

Carbine gas tubes are approximately 7.5 inches long, which means the handguards are approximately 6.5 to 7 inches long. These include the…


Mid-length gas systems have become quite popular and are most commonly used with barrels from 14 to 20 inches long. They give you a longer sight radius and reduce some of the wear and tear on the upper receiver.

Mid-length gas tubes are approximately 9.5 inches long and require a handguard around 8.5 to 9 inches long. Choices for handguards of this length include the…


Rifle-length gas tubes are generally about 13 inches long, requiring handguards ranging from 11.5 to 12 inches long.

These are usually found on rifles with barrels 20 inches in length and longer.

If you’re looking for replacement handguards for a rifle-length system, check out the

What size gas systems do you have on your AR-15? Are you planning to check out some of the options shared here? Let your fellow readers know by sharing in the comment section.

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Comments (15)

  • Anthony Rogers


    Building an AR pistol with an 11.5 barrel. What size gas tube do you all recommend


  • Jjerry


    Which size gas tube do I get for my 7in free float carbine m4 build? Im lost n don’t understand


  • Leon


    My AR has a carbine length gas system with a 16 inch barrel. Is it possible for me to add a 12 inch hand guard if I use a low profile gas block? Thank you!


  • DL


    I am not very knowledgeable on this topic but I understand rifle length gas tubes are between 15and1/8 and 15 and1/4 inch. not 13″ This is what is on my 20″ barrel and all other sights, I have looked at, who gas tubes advertise these lengths.


  • joe


    Gas tubes are long and skinny, and mount to the shoulder thing that goes up and shoots 30caliber magazine clips in like 1/2 of a second.


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