Many AR-15 enthusiasts, particularly those undertaking their first build, encounter frustrating issues with automatic cycling. A common problem reported by builders is a failure of the action to cycle completely, requiring manual operation of the charging handle after each shot, despite the rifle firing correctly. This issue often points to problems within the gas system, specifically alignment of the gas block, tube, and barrel.
The core of the issue lies in the gas system’s function: pressurized gas generated by a fired cartridge travels through the gas block, down the gas tube, and impinges on the bolt carrier group, providing the energy needed to cycle the action. If this system isn’t properly aligned, gas flow can be restricted or misdirected, leading to insufficient force to fully cycle the bolt. Understanding the intricacies of this system is crucial for diagnosing and resolving these cycling problems.
Gas System Alignment: A Common Culprit
One of the most frequent causes of cycling failures is misalignment within the gas system. As one builder explained on a forum, a misaligned gas tube can rub against the inside of the upper receiver, creating friction and hindering the bolt carrier’s movement. This rubbing reduces the efficiency of the gas transfer, preventing complete cycling. Similarly, an improperly dimpled barrel, where the gas block isn’t correctly lined up, can also disrupt gas flow.
The pressure generated within the gas system during firing is substantial. According to data from AR15.com forums, gas port pressure on a 20-inch barrel typically ranges from 13,000 to 15,000 psi. Shorter, carbine-length gas ports can experience even higher pressures, reaching 23,000 to 30,000 psi. While only about 5% of this pressure is actually needed to cycle the action, even minor misalignments can significantly impede the transfer of that necessary force.
Troubleshooting and Potential Solutions
Addressing these issues often requires disassembly and careful re-alignment of the gas block, and tube. It’s crucial to ensure the gas tube is properly seated within the gas block and that the gas block is securely attached to the barrel with the dimple correctly positioned. Some builders have found success by replacing the gas block with a new one, ensuring proper alignment during installation.
Another potential issue, as highlighted in a YouTube video discussing AR-15 cycling problems, is an insufficient gas port diameter. If the gas port is too little, it may not allow enough gas to reach the bolt carrier group, even with perfect alignment. This requires a qualified gunsmith to properly assess and potentially enlarge the gas port.
Simulating Gas Pressure for Testing
Given the difficulty of consistent range access for testing, some builders have explored methods to simulate gas pressure. One builder proposed using compressed air down the barrel to test the action’s cycling ability. However, determining the appropriate PSI to replicate the pressure generated by a fired cartridge, such as an XM855 Green Tip (62gr), is challenging. The exact PSI required to cycle the action would depend on various factors, including the specific AR-15 configuration and gas system length.
It’s important to note that attempting to simulate gas pressure requires caution and a thorough understanding of firearm safety. Removing the flash suppressor is a necessary step, and any testing should be conducted in a safe and controlled environment.
What to Watch For
For AR-15 builders experiencing cycling issues, a systematic approach to troubleshooting is essential. Start by carefully inspecting the gas block and tube alignment. If misalignment is detected, disassemble and re-align the components. If the problem persists, consider evaluating the gas port diameter and consulting with a qualified gunsmith. Continued testing and refinement are often necessary to achieve reliable automatic cycling.
Have you encountered similar cycling issues with your AR-15 build? Share your experiences and solutions in the comments below. Don’t forget to share this article with fellow AR-15 enthusiasts who may be facing similar challenges.
