Why Your AR Won’t Cycle — And What to Do About It
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Diagnosing Gas System and Extraction Issues in AR-15 and AR-10 Platforms
You’ve spent good money on a rifle — maybe it’s a custom 5.56 AR, maybe a precision AR-10 in 6.5 Creedmoor. But now it’s short-stroking. Not ejecting. Won’t lock back. Won’t run right — and it’s driving you nuts. We see this all the time at Redleg Guns. And no, it's not always the ammo.
Cycling issues are one of the most common problems our customers face with AR platforms — and one of the most misunderstood. This guide breaks down the causes and cures, step by step, so you can diagnose your AR like a pro and get it running smooth and reliable, whether suppressed, unsuppressed, or somewhere in between.
🔁 What Does “Won’t Cycle” Actually Mean?
Cycling is the full mechanical process your rifle goes through with every shot:
Round fires
Gas pushes the bolt carrier rearward
Spent case ejects
New round chambers
If any one of those steps fails — you get short-stroking, failures to eject, failures to feed, or no lock-back — you’ve got a cycling issue.
⚙️ Common Causes of Cycling Issues in AR Platforms
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 far enough?
Is your gas port properly sized for your barrel, caliber, and use case?
Carbon buildup in the gas block?
Gas block alignment 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 fast — causing premature bolt unlock, increased recoil, and excessive wear on internal parts.
What to check:
• Are you running 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 beats itself up over time. Try an H2 or H3 buffer, install an adjustable gas block, or switch to a flat wire or extra power spring to slow things down and preserve reliability. Sometimes you have to do all of these.
🔧 Gas Port Size Reference Charts
.223 / 5.56
Barrel Length | Gas System | Unsuppressed | Suppressed |
10.3" | Carbine | 0.070"–0.081" | 0.065"–0.075" |
11.5" | Carbine | 0.070"–0.078" | 0.062"–0.070" |
14.5" | Mid | 0.073"–0.078" | 0.065"–0.072" |
16" | Mid | 0.075"–0.081" | 0.068"–0.074" |
20" | Rifle | 0.090"–0.100" | 0.080"–0.090" |
✅ Note: Many factory barrels are intentionally over-gassed for reliability with weak ammo.
.300 Blackout
Barrel Length | Gas System | Supersonic | Subsonic |
8.5" | Pistol | 0.090"–0.100" | 0.110"–0.120" |
10" | Pistol | 0.093"–0.100" | 0.110"–0.125" |
16" | Carbine | 0.100"–0.120" | 0.120"+ |
⚠️ Subsonic loads often require suppressors and large ports to cycle properly.
6mm ARC / 6.5 Grendel
Barrel | Gas System | Unsuppressed | Suppressed |
16" | Mid | 0.080"–0.085" | 0.075"–0.080" |
18" | Rifle | 0.085" | 0.075"–0.080" |
20" | Rifle | 0.090" | 0.080" |
🔍 These cartridges benefit from longer dwell time and tuned buffers.
.308 Win / AR-10
Barrel | Gas System | Unsuppressed | Suppressed |
16" | Carbine | 0.080"–0.090" | 0.075"–0.080" |
18" | Mid | 0.085"–0.093" | 0.075"–0.085" |
20" | Rifle | 0.093"–0.100" | 0.085"–0.090" |
6.5 Creedmoor / AR-10
Barrel | Gas System | Unsuppressed | Suppressed |
18" | Rifle | 0.090"+ | 0.080"–0.085" |
20" | Rifle | 0.095"–0.100" | 0.085"–0.090" |
22"+ | Rifle+ | 0.100"+ | 0.090" |
💡 Use an adjustable gas block and buffer tuning to optimize suppressed 6.5CM performance.
2. Buffer and Spring Weight Mismatch
Too light, and the bolt cycles too fast.
Too heavy, and 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’s Buffer System Guide
AR-15 Buffer Reference: .223 / 5.56 NATO
Barrel Length | Gas System | Suppressed | Recommended Buffer | Spring | Notes |
10.3"–10.5" | Carbine | No | H2 | Standard or Flat Wire | Aggressive gas — H2 helps reduce recoil and bolt speed |
10.3"–10.5" | Carbine | Yes | H3 | Flat Wire or Sprinco Blue | Suppressor adds gas — go heavier and tune with gas block |
11.5" | Carbine | No | H2 | Standard or Flat Wire | Slightly more forgiving than 10.3", but still benefits from H2 |
11.5" | Carbine | Yes | H3 | Flat Wire or Blue | Suppressed 11.5" often runs hot — H3 softens recoil, aids longevity |
14.5" | Mid | No | H or H2 | Standard | Factory barrels often overgassed — H2 adds reliability |
14.5" | Mid | Yes | H2 or H3 | Flat Wire | Suppressed mid-lengths benefit from added buffer mass |
16" | Mid | No | H | Standard | Typical duty setup — H buffer keeps function reliable with most ammo |
16" | Mid | Yes | H2 | Flat Wire or Blue | Suppressor adds gas — H2 helps control recoil and wear |
18"–20" | Rifle | No | H | Rifle Spring | Smooth gas curve — minimal tuning needed |
18"–20" | Rifle | Yes | H2 | Rifle Spring | Suppressed rifle gas ARs can benefit from added resistance |
AR-15 Buffer Reference: .300 Blackout
Barrel Length | Gas System | Ammo Type | Suppressed | Recommended Buffer | Spring | Notes |
8.5"–9" | Pistol | Supersonic | No | H | Standard | Functions well with moderate buffer — not overgassed |
8.5"–9" | Pistol | Supersonic | Yes | H2 | Flat Wire | Suppressor boosts pressure — H2 smooths cycle |
8.5"–9" | Pistol | Subsonic | Yes | H2 or H3 | XP Spring or Flat Wire | Subsonic needs suppressor and generous gas — tune carefully |
16" | Carbine | Supersonic | No | H | Standard | Overgassed in some cases — H adds reliability |
16" | Carbine | Subsonic | Yes | H or H2 | Standard Spring or Flat Wire | Needs large gas port + H buffer to cycle subsonics cleanly |
⚠️ Note: Subsonic ammo will NOT always reliably cycle without a suppressor unless the gas port is very large.
AR-15 Buffer Reference: 6mm ARC / 6.5 Grendel / 22 ARC
Barrel Length | Gas System | Suppressed | Recommended Buffer | Spring | Notes |
16" | Mid | No | H2 | Standard or Flat Wire | High-pressure loads need buffer mass to avoid overcycling |
16" | Mid | Yes | H2 or H3 | Flat Wire | Suppressed ARC often overgassed — heavier buffer slows timing |
18" | Rifle | No | H2 | Standard or Flat Wire | Long dwell time works well with H2 — reliable with factory loads |
18" | Rifle | Yes | H2 | Flat Wire or Sprinco Blue | Suppressor boosts pressure — use H3 for bolt control |
20" | Rifle | No | H2 | Flat Wire | Smooth recoil, consistent lock-back |
20" | Rifle | Yes | H2 | Flat Wire | For PRS-style builds, heavier buffers help control recoil and keep timing stable |
🔍 These cartridges have sharper pressure curves and longer bullets. Tuning gas + buffer system is crucial for smooth function and accurate follow-up shots.
AR-10 .308 Win Buffer Reference
Barrel Length | Gas System | Suppressed | Recommended Buffer | Spring | Notes |
16" | Carbine | No | H2 | Standard or Flat Wire | May feel snappy — heavier buffer helps |
16" | Carbine | Yes | H3 | Sprinco Orange | Suppressed boosts gas pressure — slow it down |
18" | Mid or Rifle | No | H2 | Flat Wire | Reliable with full-mass carrier |
18" | Mid or Rifle | Yes | H3 | Sprinco Orange | Suppressed watch for early bolt unlock with hot loads |
20" | Rifle | No | H2 | Standard or Flat Wire | Long dwell time = more forgiving |
20" | Rifle | Yes | H3 or Rifle Buffer | Flat Wire or Orange | Suppressed Buffer + adjustable gas ideal for tuning |
AR-10 Buffer Reference: 6.5 Creedmoor
Barrel Length | Gas System | Suppressed | Recommended Buffer | Spring | Notes |
18" | Rifle | No | H2 or Rifle Buffer | Flat Wire | Good balance, soft recoil — watch dwell time |
18" | Rifle | Yes | H3 or Rifle Buffer | Sprinco Orange | Suppressor adds gas — tune with adjustable block |
20" | Rifle | No | Rifle Buffer | Flat Wire | Ideal setup for gas balance and consistent cycling |
20" | Rifle | Yes | H3 or Rifle Buffer | Sprinco Orange | Reduces bolt speed and manages suppressor blowback |
22"–24" | Rifle+ | Yes | Rifle Buffer or JP SCS | Flat Wire | Best for long-range builds — smoothest recoil impulse |
AR-10 Buffer Reference: .243 Winchester
Barrel Length | Gas System | Suppressed | Recommended Buffer | Spring | Notes |
18" | Rifle | No | H2 | Flat Wire | Snappy recoil with fast powder loads — tune carefully |
18" | Rifle | Yes | H3 | Sprinco Orange | Suppressor increases gas — slow bolt down to prevent early unlock |
20" | Rifle | No | H2 or Rifle Buffer | Flat Wire | Similar behavior to 6.5CM — works well with standard tuning |
20" | Rifle | Yes | H3 or Rifle Buffer | Sprinco Orange | High-pressure loads may require additional buffer mass |
22" | Rifle | Yes | Rifle Buffer | Flat Wire | Long dwell time + suppressor = easy to overgas — tune carefully |
💡 When to Use:
Heavier Buffers (H2/H3): Suppressed guns, short barrels, high-pressure loads
Extra Power Springs: Subsonic setups, fast cycling issues, lightweight BCGs
Flat Wire Springs: Smoother cycling, better durability, reduced “twang”
Lightweight Carriers: Only in race guns or precision builds — not ideal for suppressed or high-pressure setups
If you go lighter in the carrier, you must go heavier in the spring or buffer.
⚙️ JP Silent Captured Spring System (SCS)
The JP SCS is an integrated buffer system with a smooth recoil impulse, no spring noise, and tunable weights. It's ideal for:
Suppressed rifles
Precision AR-10s
Competition guns
Just note: 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 extractor
🎯 Use a high-quality, properly staked, HPT(High Pressure Tested) and MPI(Magnetic Particle Inspection) BCG — preferably nitrided or nickel boron coated.
4. Ammo Problems
Don’t overlook the obvious — if your gun only malfunctions with one kind of ammo, it’s probably the ammo.
Check:
Velocity and pressure (chronograph reloads)
Steel vs brass casing
Case dimensions and shoulder set-back
5. Extractor & Chamber Problems
Sometimes it’s not gas or buffers — it’s mechanical.
Check:
Extractor spring tension and O-ring
Chamber cleanliness
Tool marks or tight chamber
Headspace issue
🧠 Final Thoughts
Cycling issues are rarely caused by just one thing. It's a system — and the good news is, once it's dialed in, your rifle will run smooth, reliable, and consistent.
At Redleg Guns, we don’t just slap parts together. We diagnose, build, and tune with purpose — because our customers expect rifles that work every time.
📣 Need Help Diagnosing Your AR?
📞 Call us at (507) 677-6007
📧 Email: info@redlegguns.com
🛠️ Or schedule a bench inspection at RedlegGuns.com
Let’s get your rifle running right — the Redleg way.