Why Your AR Won’t Cycle And What to Do About It

Diagnosing Gas System and Extraction Issues in AR-15 and AR-10 Platforms

You’ve invested in a quality rifle whether it’s a custom 5.56 AR or a precision AR-10 in 6.5 Creedmoor. But now, it’s short-stroking, not ejecting, and won’t lock back. It’s frustrating, right? At Redleg Guns, we encounter these issues frequently. And no, it’s not always the ammo.

Cycling issues are among the most common problems our customers face with AR platforms. They are also one of the most misunderstood. This guide breaks down the causes and solutions step by step. You’ll learn how to diagnose your AR like a pro and get it running smoothly and reliably, whether suppressed, unsuppressed, or somewhere in between.

🔁 What Does “Won’t Cycle” Actually Mean?

Cycling is the complete mechanical process your rifle undergoes with every shot:

1. Round fires.

2. Gas pushes the bolt carrier rearward.

3. Spent case ejects.

4. New round chambers.

   
   

If any of these steps fail, you may experience short-stroking, failures to eject, failures to feed, or no lock-back. This indicates a cycling issue.

Where is your fired brass landing?

⚙️ AR won’t cycle, Common Causes of Cycling Issues

1. Gas System Misconfiguration

If your rifle is under-gassed, the bolt won’t travel far enough to complete the cycle.

What to check:

• Is your adjustable gas block open wide enough?

• Is your gas port properly sized for your barrel, caliber, and use case?

• Is there carbon buildup in the gas block?

• Is the gas block aligned over the barrel port?

  
  

🧠 Redleg Tip: Start with the gas block wide open. Once function is confirmed, dial it back for optimal performance.

If your rifle is over-gassed, the bolt carrier may cycle too quickly. This can cause premature bolt unlock, increased recoil, and excessive wear on internal parts.

What to check:

• Are you using a suppressor without tuning the gas system?

• Is your buffer too light for your setup?

• Are you using high-pressure ammo with a wide-open gas block?

• Is your ejection pattern forward (1–2 o’clock), indicating early unlock?

  
  

🧠 Redleg Tip: An over-gassed rifle can damage itself over time. Consider using an H2 or H3 buffer, installing an adjustable gas block, or switching to a flat wire or extra power spring to slow things down and maintain reliability. Sometimes, you may need to do all of these.

As long as you have a drill bit that hasn't been damaged from use. This is a quick and easy way to check your gas port hole size.

🔧 Gas Port Size Reference Charts

🟢 .223 / 5.56 NATO

Barrel (in.)	Gas System	Unsuppressed Port	Suppressed Port	Notes
10.3	Carbine	0.070"–0.081"	0.065"–0.075"	CQB, often over-gassed from factory
11.5	Carbine	0.070"–0.078"	0.062"–0.070"	Ideal balance for reliability
14.5	Mid	0.073"–0.078"	0.065"–0.072"	Smooth cycling for duty/defense
16	Mid	0.075"–0.081"	0.068"–0.074"	Most versatile configuration
20	Rifle	0.090"–0.100"	0.080"–0.090"	Long dwell time tune with buffer

💡 Note: Most factory AR barrels are intentionally over-gassed for reliability with weak ammo.

🟠 .300 Blackout

Barrel Length	Gas System	Ammo Type	Unsuppressed Port	Suppressed Port	Notes
7.5"–8.5"	Pistol	Supersonic	0.090"–0.100"	0.086"–0.094"	Reliable cycling for most supersonic ammo
8.5"–9"	Pistol	Subsonic	0.110"–0.125"	0.093"–0.106"	Subsonic often needs suppressor to cycle
10"	Pistol	Supersonic	0.086"–0.094"	0.080"–0.090"	Ideal general-purpose Blackout setup
16"	Carbine	Supersonic	0.093"–0.100"	0.086"–0.092"	Over-gassed without suppressor tune with H2 buffer
16"	Carbine	Subsonic	0.110"–0.125"	0.093"–0.106"	Only cycles subsonic with suppressor

⚠️ Subsonic loads often require suppressors and large ports to cycle properly.

🔵 6mm ARC

Barrel Length	Gas System	Unsuppressed Port	Suppressed Port	Notes
12.5"	Carbine	0.085"–0.090"	0.080"–0.085"	Short dwell, needs careful tuning
14.5"	Mid	0.080"–0.085"	0.075"–0.080"	Best balance for field rifles
16"	Mid	0.078"–0.083"	0.072"–0.078"	Great all-around reliability
18"	Rifle	0.076"–0.081"	0.070"–0.076"	Long dwell; smooth recoil impulse
20"	Rifle	0.074"–0.078"	0.068"–0.074"	Excellent precision setup

🔍 These cartridges benefit from longer dwell times and tuned buffers.

🔵 6.5 Grendel

Barrel Length	Gas System	Unsuppressed Port	Suppressed Port	Notes
12.5"	Carbine	0.089"–0.094"	0.080"–0.086"	Compact builds ensure solid gas seal
14.5"	Mid	0.083"–0.089"	0.076"–0.083"	Balanced setup for all loads
16"	Mid	0.081"–0.086"	0.074"–0.081"	Great reliability across brands
18"	Rifle	0.078"–0.083"	0.070"–0.078"	Excellent for accuracy builds
20"	Rifle	0.076"–0.081"	0.068"–0.075"	Tuned for long-range performance

🧠 Grendel thrives with moderate ports and heavier buffers to control pressure spikes.

🔴 .308 Winchester / 6.5 Creedmoor (AR-10)

Barrel Length	Gas System	Unsuppressed Port	Suppressed Port	Notes
14.5"	Carbine	0.085"–0.093"	0.080"–0.088"	Short dwell needs H3 or SCS buffer
16"	Mid	0.080"–0.086"	0.075"–0.082"	Suppressor-friendly tuning
18"	Rifle	0.078"–0.084"	0.072"–0.079"	Common match configuration
20"	Rifle	0.076"–0.082"	0.070"–0.076"	Long dwell, tune with buffer mass
22"	Rifle	0.074"–0.080"	0.068"–0.074"	Precision and PRS ideal setup

💡 Larger-frame rifles benefit from lower port pressures and heavier reciprocating mass.

2. Buffer and Spring Weight Mismatch

If the buffer is too light, the bolt cycles too quickly. If it’s too heavy, it short-strokes.

Common fixes:

• Use an H2 or H3 buffer in over-gassed setups or suppressed builds.

• Match spring type to your gas system and buffer tube length.

• Upgrade to extra power or flat wire springs for better control.

  
  

🧭 Redleg Gunsmithing Recommendations

Platform	Best Starting Point	Buffer Recommendation	Spring Recommendation
AR-15 5.56	0.075" port, H2 buffer	H2	Flat Wire
.300 BLK (Suppressed)	0.093" port, H2 buffer	H2	Flat Wire
6mm ARC	0.080" port, H2 buffer	H2	Standard
6.5 Grendel	0.081" port, H2 buffer	H2	Flat Wire
AR-10 .308 / 6.5CM	0.078" port, H3 buffer	H3	Flat Wire

🔧 Always test suppressed vs. unsuppressed performance. Slightly under-gas and tune up never the reverse.

⚙️ JP Silent Captured Spring System (SCS)

The JP SCS is an integrated buffer system that provides a smooth recoil impulse, eliminates spring noise, and offers tunable weights. It’s ideal for:

• Suppressed rifles

• Precision AR-10s

• Competition guns

  
  

Just keep in mind: it costs more, requires tuning, and may not fit all receivers.

3. Bolt Carrier Group (BCG) Issues

Inspect for:

• Gas key staking

• Clean, lubricated rails and bolt tail

• Good gas rings (no binding or wear)

• No carbon caking under the extractor

  
  

🎯 Use a high-quality, properly staked, HPT (High Pressure Tested) and MPI (Magnetic Particle Inspection) BCG — preferably nitrided or nickel boron coated.

Gas Key Staking

4. Ammo Problems

Don’t overlook the obvious. If your gun only malfunctions with one kind of ammo, it’s likely the ammo.

Check:

• Velocity and pressure (chronograph reloads)

• Steel vs. brass casing

• Case dimensions and shoulder set-back

  
  

5. Extractor & Chamber Problems

Sometimes, the issue isn’t gas or buffers; it’s mechanical.

Check:

• Extractor spring tension and O-ring

• Chamber cleanliness

• Tool marks or tight chamber

• Headspace issue

  
  

Extractor and Components

Chamber with Heavy Tool Marks

🧠 Final Thoughts

Cycling issues are rarely caused by just one factor. It’s a system. The good news is that once everything is dialed in, your rifle will run smoothly, reliably, and consistently.

At Redleg Guns, we don’t just slap parts together. We diagnose, build, and tune with purpose. Our customers expect rifles that work every time.

🎯 Take the Next Step

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