Why Your AR-15 Won't Cycle — And How to Fix It
Posted by Faxon Firearms Staff on Apr 7th 2026
A rifle that won't run isn't a rifle — it's an expensive liability. Cycling failures are among the most common issues we hear about from our customers, and in the overwhelming majority of cases, the root cause is not the barrel. It's the gas system, the buffer, the ammunition, or a combination of all three.
At Faxon Firearms, we manufacture barrels to exacting tolerances — but even a perfect barrel can fail to cycle in an improperly assembled or poorly tuned rifle. This post breaks down the most common AR-15 cycling failures, explains what's happening inside the action when they occur, and gives you a clear path to diagnosing and resolving the issue before you ever consider sending anything back.
The Root of Every Cycling Problem
Every AR-15 cycling failure, without exception, is a disruption in gas timing. When a round fires, propellant gases travel down the bore, enter the gas port, travel through the gas tube, and drive the bolt carrier group rearward. That rearward motion ejects the spent case, cocks the hammer, and compresses the buffer spring. The spring then returns the BCG forward, stripping a fresh round from the magazine and chambering it.
Disrupt that sequence anywhere — too much gas, too little gas, too heavy a buffer, a kinked gas tube, an exhausted magazine spring — and you get a malfunction. The specific type of malfunction tells you exactly where in the sequence the disruption is occurring. That's the insight most shooters miss: your malfunctions are diagnostic data.
Your malfunctions are diagnostic data. The symptom tells you where in the gas cycle the system broke down.
The Four Most Common Failures
Before you can fix a cycling issue, you have to name it correctly. Here are the four failure modes we see most often, what they look and feel like, and what they're telling you.
A fresh round fails to enter the chamber after the previous case was ejected. The bolt closes on an empty chamber or jams on a partially chambered round. Most often caused by under-gassing, a weak or damaged magazine, or undercharged/weak ammunition. Start with the magazine before assuming the gas system is at fault.
A spent case remains in or around the chamber after firing. The classic "stovepipe" — a case standing upright in the ejection port, pinched by the bolt — is almost always a sign of under-gassing. The bolt is not traveling far enough rearward to fully clear the case before returning forward.
The BCG travels rearward but not far enough to fully cock the hammer. The trigger resets but the hammer doesn't follow through. Common in suppressed setups running too light a buffer, or in extreme cold where lubricant thickens.
The BCG travels rearward with so much force that it bounces off the buffer before the trigger has reset. Results in hammer-follow, failure to reset, or double-feeds. Suppressor use is the most common trigger — adding a can to a standard-tuned rifle dramatically increases gas back-pressure.
The First Three Things to Check
Before adjusting the gas system, replacing components, or initiating a warranty claim, work through these three checks in order. They resolve the majority of cycling complaints we receive — and they cost nothing.
A dirty or dry AR-15 is the single most common source of cycling failures. Carbon buildup in the gas key, a dry bolt carrier, or debris in the chamber can cause every symptom on the list above. Clean the BCG thoroughly — paying specific attention to the gas key and its interior — and apply a quality lubricant to all moving contact surfaces before investigating further.
Magazine springs, followers, and feed lips cause more FTF and FTE issues than gas systems do. Test with at least two or three known-good magazines. Simultaneously, test with name-brand, standard-pressure factory ammunition — not handloads or steel-case surplus. If the issue appears with only one magazine or ammo type, you've found your culprit.
If you're running a suppressor, take it off and fire the rifle unsuppressed. If the issue disappears, the suppressor is adding back-pressure that the rifle is not currently tuned to handle. This is not a defect — it is physics. The solution is an adjustable gas block, a heavier buffer, or both.
Reading Your Ejection Pattern
One of the fastest diagnostic tools available to any shooter is also the most overlooked: where is your brass landing? Ejection pattern is a direct readout of bolt velocity — and bolt velocity tells you whether your gas system is appropriately tuned.
Think of a clock face, with the muzzle pointing at 12 o'clock. In a properly tuned rifle, ejected cases should land consistently around the 3 to 4 o'clock position, approximately 6 to 10 feet from the shooter. Deviation from that pattern is information:
Cases landing at 1–2 o'clock (forward of the shooter): Over-gassed. Add buffer weight or reduce gas flow with an adjustable gas block.
Cases landing at 4–5 o'clock or dropping at your feet: Under-gassed. Reduce buffer weight or increase gas flow.
Stovepipe jams: Classic under-gassing. The case is not clearing the ejection port before the bolt returns forward.
The Buffer — Your Most Accessible Tuning Tool
Most shooters overlook the buffer as a tuning variable. It shouldn't be — it's the lowest-cost, most reversible adjustment in the AR system. A heavier buffer slows rearward BCG travel, which is what you want in an over-gassed setup. A lighter buffer lets the BCG cycle more freely, which helps in under-gassed applications.
For most 5.56/.223 builds with a 16" barrel, an H (3.8 oz) buffer is a solid starting point. Add a suppressor, and stepping to an H2 (4.6 oz) or H3 (5.4 oz) is often all that's needed to tame the increased back-pressure. The simple rule: start with the lightest buffer that achieves reliable function, then add weight as needed. Always verify last-round bolt lockback — if the bolt won't lock back on an empty magazine, you've gone too heavy for your available gas volume.
Suppressed Use: Adjust the Gas, Not the Barrel
The single most common source of cycling complaints we receive from customers running suppressors is over-gassing — and the single most common misdiagnosis is "defective barrel." A suppressor changes the pressure environment of the rifle fundamentally. Gases that would exit freely at the muzzle are now slowed and partially reflected back toward the action. A rifle perfectly tuned without a can will almost always run over-gassed with one attached.
The correct solution is an adjustable gas block. Faxon offers the Faxon Patented Adjustable 3 Screw Low Profile Gas Block, available in .750" and .625" journal diameters (with .875" coming soon), specifically designed for this application. Its detent-based adjustment mechanism holds its position under firing, unlike bare set-screw designs that can shift over time. Paired with a Faxon barrel, it eliminates the guesswork of third-party fitment entirely.
When tuning for suppressed use, reduce gas flow in small increments, testing after each adjustment, and always verify reliable last-round bolt lockback with your lightest expected ammunition before considering the rifle finalized.
300 Blackout: A Special Case
If you're running a 300 BLK build, there's one cycling behavior that trips up a significant number of first-time owners: subsonic ammunition is designed to be shot suppressed. A 220gr subsonic load traveling at roughly 1,050 fps simply does not generate enough gas pressure to reliably cycle an unsuppressed rifle. This is not a defect — it is the intended design of the cartridge.
If you're shooting 300 BLK subsonic loads unsuppressed and experiencing short-stroking or failure to feed, the rifle is performing exactly as it should. The solution is to add a suppressor, not to modify the rifle. Supersonic loads — typically 115–125gr bullets at 2,100–2,300 fps — will cycle unsuppressed without issue.
When to Contact Us
We want to help you solve your problem — and in most cases, the solution is something you can implement in your garage in under an hour. But there are situations that genuinely warrant a warranty or RMA conversation with our team.
If you have cleaned and lubricated the rifle, confirmed the issue across multiple magazines and factory ammunition brands, removed any suppressor and retested, verified the gas tube is clear and properly seated, and are still experiencing consistent cycling failures — contact us. Have your order number, barrel model, approximate round count, and a clear description of the specific failure mode ready. Our team will move quickly.
What we ask is that you complete the diagnostic steps first. Not because we're trying to avoid warranty work — but because the answer is almost always faster than shipping a barrel back and forth. Our full AR-15 Gas System Tuning & Troubleshooting Guide includes a Pre-RMA Checklist that walks through every step our Customer Service team will ask about anyway. Work through it first. More often than not, you'll find your answer before you reach the bottom.