How to Select the Correct Gas Control for Your Carbine

Selecting the right model RIFLESPEED Gas Control for your AR15 or AR10 is a simple process that requires only a minute of your time. To simplify matters if you already know the measurements below, refer to the Common Configurations charts HERE for most configurations. We also have an online calculator that lets you avoid all of the hard math (like addition and subtraction of small numbers) involved with this process. A video of this process is available here https://youtu.be/HlapqlbH4oo and is also posted below.

Here's how it's done:

  • Determine which gas system your carbine uses by measuring the distance from the front of your upper receiver to the shoulder behind the front-sight-base journal. Measurements to the nearest 1/8" with a ruler, tape measure, or yardstick are plenty accurate here. The most common gas system lengths are:
    • Pistol - 4.3 inches from receiver to gas block journal
    • Carbine - 7.3 inches from receiver to gas block journal
    • Midlength - 9.3 inches from receiver to gas block journal (shown in the image below)
    • Rifle - 12.6 inches from receiver to gas block journal
  • You'll also need to know the diameter of your gas block journal. 0.750 inches is the most common size. Lightweight "Pencil" barrels have a diameter of 0.625 inches. Gas Controls for 0.750 inch journals will have model numbers beginning in RS75 while those sized for 0.625 inch journals will begin with RS62.


Measure Gas System Length by finding the distance from the front of your receiver to the rear of your gas block

Measure Gas System Length by finding the distance from the front of your receiver to the rear of your gas block as pictured above
Measure Gas System Length by finding the distance from the front of your receiver to the rear of your gas block as pictured above

  • Next determine the length of your handguard by measuring the distance from the front of your upper receiver to the end of the handguard at its forward-most point. If the front of your handguard is cut on an angle, measure to the point nearest the muzzle. Measurements to the nearest 1/8" with a ruler, tape measure, or yardstick are plenty accurate here as well. The handguard pictured below measures 13-inches long. 

Measure Handguard Length


  • Your final measurement is from the front of your upper receiver to the end of your barrel, including the muzzle threads. Our online calculator is designed to calculate for barrel length including muzzle threads so there's no need to subtract the 0.6-inches of muzzle threads on an AR barrel. In the picture above we see that the barrel is 14.5-inches long. If you have a muzzle device or suppressor mount that covers part of the barrel behind the muzzle threads you’ll need to subtract the overhang from your barrel length. Common examples of this would be reflex-style suppressor like the Surefire  FA762SS.

The easiest way to determine the correct Gas Control for your setup is to enter the measurements you've just collected into our Configurator. Once you’ve input your measurements, the Configurator will provide color-coded results to show which RIFLESPEED Gas Control model or models will fit your carbine. Using the measurements obtained through the process described above we now know that this carbine has a midlength gas system under a 13-inch handguard on a 14.5-inch barrel. The diameter of the gas block journal is 0.750 inches. The Configurator tells us that the correct model Gas Control for this carbine the model RS7543.

If more than one Gas Control model fits your carbine, we suggest going with the shorter option. The ideal fitment leaves about one inch of the Control Knob exposed in front of the handguard. There’s nothing wrong with having more of the Control Knob exposed if you like that look or frequently make adjustments to your Gas Control in arctic weather while wearing mittens or extremely heavy gloves. More exposure allows you grasp the Control Knob with more fingers when needed.

If you’re unable to use the Configurator you can determine the correct model Gas Control for your carbine by measuring the distance from the shoulder behind the gas block journal on your barrel or the back of your existing gas block to the end of your handguard. Add 0.9 inches to this measurement. The sum of these two numbers is your ideal Gas Control length. You must also confirm that there’s enough room for this Gas Control to be mounted on your barrel by measuring the distance from the shoulder behind your gas-block journal or the back of your current gas block to the back of your muzzle device. Your Gas Control must be shorter than this measurement. 

If you can’t find a Gas Control that fits your carbine, please contact us for assistance. Include the measurements you obtained from the process above and send as much information about your setup as possible. We’ll do our best to get you setup with the right Gas Control.


Above Image: This AR is equipped with a 10.5-inch barrel, carbine-length gas system, and 8" handguard. Gas Control is RIFLESPEED model RS7519


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