What is a Mid Length Gas System?
To appreciate the role of the mid length gas tube length, one must first understand the basics of the AR-15’s gas system. This system harnesses the expanding gases generated by the fired round to cycle the action, meaning to eject the spent casing, chamber a fresh round, and prepare the rifle for the next shot. It’s a clever, self-regulating mechanism at the heart of the AR-15’s semi-automatic function.
The gas system works by tapping a portion of the high-pressure gas from the barrel after the bullet has passed the gas port. This gas is then channeled through a gas tube, which is a narrow, metal tube, and into the bolt carrier group. The gas then pushes the bolt carrier rearward, unlocking the bolt, extracting the spent cartridge, and compressing the buffer spring. The compressed buffer spring then returns the bolt carrier forward, stripping a fresh round from the magazine, chambering it, and locking the bolt.
The length of the gas system, primarily determined by the positioning of the gas block on the barrel, has a significant impact on the timing and operation of this cycle. There are three primary gas system lengths: carbine, mid-length, and rifle. A carbine-length gas system features a gas block and port closer to the chamber, while a rifle-length gas system places them further away. The mid length gas tube length, as the name suggests, occupies a position between the two, offering a compromise between the advantages of both.
The mid-length system, in essence, utilizes a gas block and gas port that are situated further down the barrel compared to the carbine length, but closer to the chamber than the rifle length. This strategic placement is key to the benefits the system offers.
The evolution of gas system lengths is a story of trial and error, with designers seeking the optimal balance of performance and reliability. The carbine length was the initial design, but often, the carbine length was over-gassed, leading to increased recoil and stress on the components. The rifle length provided smoother operation due to its longer dwell time, but resulted in a longer overall platform. The mid length gas tube length emerged as an attempt to balance these competing factors, offering a smoother, more reliable system while still maintaining a manageable overall length, and is now a popular choice for many AR-15 builds.
Benefits of a Mid Length Gas System
The mid length gas tube length provides several advantages compared to other configurations, particularly carbine-length systems. These benefits contribute to a more enjoyable and reliable shooting experience.
One of the most significant advantages is the reduction in felt recoil. The longer gas system, with its strategically placed gas port, allows for a more gradual build-up of gas pressure, smoothing out the recoil impulse. This results in a softer, more manageable recoil, allowing for faster follow-up shots and less shooter fatigue. The gentler push, versus the sharper kick of a carbine system, makes a real difference, especially in longer shooting sessions or when firing rapidly. This can also result in an easier time staying on target during rapid fire.
Another key benefit is improved reliability. The mid length gas tube length helps to refine the timing of the gas cycle. This is because the bullet travels a longer distance down the barrel before the gas is tapped. This longer travel time allows for a greater pressure drop. The result is that the gas can enter the bolt carrier at the right time, leading to a smoother and more efficient extraction and ejection of spent casings. The smoother cycle reduces stress on the bolt, extractor, and other components, ultimately leading to enhanced longevity.
Furthermore, a well-designed and properly implemented mid-length system typically puts less stress on the internal components of the rifle compared to a carbine-length system. This is because the slower, more controlled cycling reduces the violent impacts on the bolt carrier group and buffer system. The slower velocity of the bolt carrier group also means it is less likely to be “smacked” against the receiver extension, which can lead to malfunctions. The reduction in wear and tear contributes to a longer lifespan for parts like the bolt, buffer spring, and other critical components.
The mid length gas tube length is, as many recognize, the perfect middle ground between rifle and carbine systems. The longer system provides a smoother operation and more balanced feel without adding excessive overall length, making it a practical choice for both tactical applications and recreational shooting. The length of the gas system is a key factor in determining overall handling and balance.
Measuring Your Gas Tube Length
Choosing the right mid length gas tube length is crucial for the proper function and reliability of your AR-15. The measurement needs to be precise to ensure a smooth and efficient gas cycle.
Before you begin, gather the necessary tools: a reliable ruler or calipers, and potentially a pencil or marker to make notes.
Here’s a step-by-step guide to accurately measure the gas tube length on your AR-15:
First, the measurement will be taken from the front edge of the upper receiver, where the gas tube enters, to the center of the gas block, where the tube attaches. You can measure the total length of the gas tube using a ruler or calipers.
A note on precision is important: even small deviations in measurement can lead to cycling issues. This is because the gas tube’s length directly affects the timing of the gas cycle. A slightly too-short tube will not allow enough gas pressure to cycle the action reliably. A slightly too-long tube can lead to binding or excessive wear. If in doubt, opt for a measurement slightly longer than what you think you need.
Accurate measurement, therefore, is the foundation of proper functioning and reliable operation.
Common Mid Length Gas Tube Lengths
While there might be minor variations between manufacturers, the mid length gas tube length typically adheres to a standard length.
The industry standard is usually around a specific length, which is measured from the shoulder of the gas tube to the pin that holds it in place. However, the specific length that works best depends on barrel length and manufacturer. For example, some manufacturers may have a barrel design that necessitates slightly different mid length gas tube length.
One of the best ways to ensure proper fit is to compare your existing tube against what is available and confirm the measurements.
It is advisable to know where you will be obtaining the parts and any of their requirements.
Potential Issues and Troubleshooting
Even with careful measurement and selection, issues can arise. Understanding potential problems related to mid length gas tube length and how to troubleshoot them can save time and frustration.
A gas tube that is too short will often lead to short-stroking, a situation where the bolt carrier does not travel far enough rearward to complete the cycle. This can result in failure to extract spent casings, failure to feed fresh rounds, and the bolt not locking back on an empty magazine.
Conversely, a gas tube that is too long can cause binding and wear. The tube can become bent, impacting the gas block. As a result, it will cause the bolt carrier to experience excessive wear and tear.
If you encounter cycling issues, try some basic troubleshooting steps. First, check for gas leaks. Carefully inspect the connections at the gas block and the upper receiver for any signs of gas escaping. Any leakage could cause the cycling to become unstable.
Next, evaluate your buffer weight and spring. The buffer weight and spring work in tandem with the gas system, and if these are out of balance, it can lead to malfunctions. You might need to try a heavier or lighter buffer, or a different spring, to optimize the system.
Finally, inspect the gas block alignment. The gas block needs to be perfectly aligned with the gas port on the barrel. A misalignment, however slight, can disrupt the flow of gas and cause cycling problems. Ensure the gas block is properly installed and tightened and that the gas tube is seated correctly.
Considerations When Choosing a Mid Length Gas Tube
Beyond the exact measurement of the mid length gas tube length, several other factors warrant consideration when selecting a replacement or building a new AR-15.
The barrel length plays a pivotal role in gas system selection. Mid-length systems are generally preferred for barrels from about 16 inches up to the 18-inch range. For barrels shorter than 16 inches, a carbine-length system might be a better fit, though mid-length systems with adjustable gas blocks can still work. For longer barrels, a rifle-length system might offer the best performance.
Gas block compatibility is another critical consideration. The gas block must be compatible with the gas tube, allowing the tube to seat securely and seal properly. The gas tube will need to go into the block smoothly and remain secure. Ensure you choose a gas block designed for the straight gas tube.
The quality and materials of the gas tube are equally important. Stainless steel gas tubes offer superior corrosion resistance compared to standard carbon steel. Some tubes are coated with coatings such as melonite, which further enhances durability and resistance to wear. A quality gas tube will ensure greater reliability and will last longer.
Finally, consider the reputation of the manufacturer. Choosing a gas tube from a reputable manufacturer known for quality components will minimize the risk of defects and ensure the gas tube meets the necessary performance specifications.
Conclusion
The mid length gas tube length is more than just a component; it’s a crucial element in the AR-15’s performance equation. Understanding its role, selecting the correct length, and recognizing the potential issues are essential steps for any AR-15 owner who seeks to optimize their rifle’s functionality and reliability.
By choosing the right mid length gas tube length, you’re taking a significant step toward achieving a smoother recoil impulse, enhanced reliability, and a more enjoyable shooting experience. It helps the AR-15 fulfill its potential as a versatile and dependable platform. Therefore, take the time to measure carefully and consider the factors outlined in this article to ensure your rifle performs at its best.
