AR-15s are gas-operated rifles that rely on gasses produced during firing to generate the force needed to cycle the bolt. These vapors flow through a series of components called the gas system, with the main parts being the gas block, gas tube and gas key.
Gas systems are available in carbine, mid and rifle-length options. If you are building a new AR-15, switching to a different-sized barrel or looking to improve performance, you need to make sure your system is the right length. This post will compare carbine- vs. mid- vs. rifle-length gas systems to help you make the right decision.
WHY DOES GAS SYSTEM LENGTH MATTER?
In an AR-15, the gas block is located up by the front sight and connects to the bolt carrier group (BCG) through a gas tube concealed underneath the handguard. Since the gas system runs across most of the upper receiver, you'll gain the best results when you use one made in the correct size. Here is what can happen if you:
- Go too short: If your rifle has a gas system that is too short, you'll have too much gas flowing back into your receiver. When you over-gas an AR-15, it creates more recoil, putting extra wear on you and your components as well as dirtying your gun.
- Go too long: When you use a gas system that is too long, you will prevent enough gas from making its way back in. Without enough force, the BCG will have trouble extracting casings and chambering the next round.
CHOOSING THE CORRECT GAS SYSTEM LENGTH
In addition to the impact the right gas tube has on the gun's function, gas systems are compatible with different-sized handguards. If your gas system is too long, it may not even fit on the rifle. The good news is that choosing the right sized gas system is simple:
GAS PORT DISTANCE (From Gas Port To Upper Receiver):
- Pistol-length gas systems: The pistol length gas system is the shortest of the gas systems and is on average only 4.3 inches.
- Carbine-length gas systems: A carbine length gas system is the most common and has a gas port distance about 7.3 inches. AR-15s with shorter 10-16-inch barrels function their best when paired with a carbine-length gas system.
- Mid-length gas systems: Mid-length systems are a little bit longer and measure in at approximately 9.3 inches. Carbines with barrels 14 to 20 inches long will deliver optimal results with mid-length gas systems.
- Rifle-length gas system: The longest of the three, rifle-length gas systems has a gas port distance of 12.65 inches long. You should install rifle-length gas systems on marksman-style AR-15s with barrels 20 inches or longer.
Since carbine- and mid-length gas systems measure similarly, bear in mind that you'll get better operation when the barrel length is closer to the middle of the functional range — a mid-length setup will better serve an 18-inch barrel than the carbine variety.
*Please note that the above gas system recommendation is for AR-15 chambered in 5.56 NATO or .223 Rem. Most 300BLK barrel uses pistol-length gas system regardless of the actual barrel length in most cases.
OTHER THINGS TO THINK ABOUT
There's more to getting the most from an AR-15 gas system than length. To get the best results when you pull the trigger, make sure you also consider your:
- Buffer weight: Your buffer weight can affect the performance of your gas system. While heavier buffers are great for absorbing recoil, you need to make sure your gas system is strong enough to power it. If you go too light, you'll wind up taking more impact when you fire and putting extra wear on your rifle. Find one that provides a balance.
- Gas block: If you still have the stock gas block that came with your rifle, you're missing out on performance. Aftermarket gas blocks are easy to install, and an adjustable gas block offers several advantages. With an adjustable gas block, you can control the exact amount of pressure channeled back through your system.
- Ammunition type: Even if you're loyal to a brand, there are still many types of ammo out there you can use with an AR-15. Heavier bullets take longer to leave the barrel, increasing dwell time and building extra gas pressure. If your bullets are too light, they can leave the barrel before you build enough pressure to cycle the next round.
TUNE YOUR AR-15 GAS SYSTEM WITH PARTS FROM WING TACTICAL
Wing Tactical is a veteran-owned company and your online source for all the parts you need to build your ideal AR-15 gas system. We also shoot, and we can help you choose all the right parts based on your weapon type, your performance goals and how you want your build to look. Ready to get started? Send us an email and let us know what you have in mind.