AR-15 Troubleshooting

Updated June 19th, 2015

Troubleshooting a previously working rifle

Bolt assembly fails to lock rear after firing last round

Inspect Remedy
Dirty or corroded bolt latch Clean.
Inspect for restricted movement of bolt catch Disassemble and clean
Inspect for broken bolt catch Replace bolt catch
Inspect for weak or broken bolt catch spring Replace bolt catch spring
Inspect magazine follower Replace magazine
Determine if magazine spring is weak Replace magazine
Inspect magazine feed lips for bends or breaks Replace magazine
Determine if follower binds during operation Replace magazine

Bolt Carrier Hangs Up

Inspect Remedy
Round Jammed between bolt and charging handle and / or double feed. Remove magazine, push on bottom of bolt latch, bang rifle butt on the ground bolt should lock to rear. Round should fall through bottom of magazine.

Bolt Wont Unlock

Dirty or Burred Bolt See gunsmith

Double Feed

Inspect Remedy
Dirty or Burred Bolt See gunsmith

Double Firing

Inspect Remedy
Perform function test If fails, continue with troubleshooting otherwise hold rifle securely against shoulder when firing.
Inspect for worn or broken trigger notch of hammer Replace hammer
Inspect for worn or broken disconnector hook of hammer Replace hammer
Inspect for worn hammer or trigger pin hole Replace lower receiver
Inspect for defective semi-automatic disconnector Replace semi-automatic disconnector
Inspect for worn or broken trigger Replace trigger

Failure to chamber

Inspect Remedy
Dirt, corrosion or carbon buildup in barrel locking lugs Clean lugs
Carbon in chamber or on gas tube Clean.
Inspect for weak or broken action spring Replace action spring

Failure to cock

Inspect Remedy
Inspect for worn or broken disconnector hook Replace disconnector
Inspect for weak broken or missing disconnector springs Replace disconnector springs
Inspect for worn or broken hammer trigger notch Replace hammer
Inspect for worn or broken hammer disconnector hook Replace hammer
Inspect for worn or broken trigger nose or trigger spring Replace trigger or defective trigger spring
Check for short stroking see short stroking troubleshooting

Failure to eject

Inspect Remedy
Determine if ejector is stuck in bolt body Disassemble and clean
Inspect for broken ejector Replace ejector
Inspect for weak or broken spring Replace ejector spring
Check for short stroking see short stroking troubleshooting

Failure to extract

Inspect Remedy
Fouling or carbon in extractor recess or lip Clean
Carbon In Chamber Clean Chamber
Frozen Extractor Remove and Clean
Restricted buffer assembly Remove and clean
Restricted movement of bolt carrier group Remove, clean and lube. Make sure gas tube fits freely into carrier
Broken Extractor Spring Replace

Failure to feed

Inspect Remedy
Magazine not fully seated Adjust mag catch or reseat
Determine if magazine catch is out of adjustment adjust magazine catch
Dirty Magazine Clean
Defective Magazine Replace
Inspect for defective magazine catch Replace magazine catch
Inspect for weak or broken magazine catch spring Replace magazine catch spring
Check for short stroking see short stroking troubleshooting
Action of buffer assembly is restricted Take out buffer and spring and clean
Too Many Rounds In Magazine Take out excess

Failure to fire

Inspect Remedy
check for improper assembly of hammer spring assemble properly
Too much carbon on firing pin or in firing pin recess Clean
Determine if selector lever is frozen in safe position Disassemble and clean
Selector Lever on Safe Put it on Fire
Defective Ammo Remove and discard
Inspect for carbon buildup  remove cartridge extractor and clean
Inspect for broken firing pin  Replace firing pin
Inspect for broken or missing firring pin retaining pin Replace firing pin retaining pin
Inspect for broken hammer Replace hammer
Inspect for broken hammer spring Replace hammer spring
Improper Assembly of firing pin Retaining pin goes n back of large shoulder of firing pin
Too Much Oil In Firing Pin Recess Wipe clean with pipe cleaner

Failure to lock

Inspect Remedy
Inspect for improperly assembled extractor spring assembly Assemble correctly
Inspect for loose screws on bolt carrier key Reassemble using new screws
Inspect for weak or broken action spring Replace action spring
Inspect for missing bolt cam pin Replace bolt cam pin
Inspect for damaged bolt carrier key Replace bolt carrier key
Inspect for bent gas tube Replace gas tube
Check for short stroking See short stroking troubleshooting

Failure to unlock

Inspect Remedy
Inspect for burred locking lugs on bolt assembly Remove burrs
Inspect for burred lugs on barrel extension Remove burrs
check for short stroking See short stroking troubleshooting

Fires with selector on safe or when trigger is released with lever on semi

Inspect Remedy
Inspect for defective selector Replace selector
Inspect for worn or broken rear portion of trigger Replace trigger

Hammer pin walks

determine if it walks or works loose during firing or of hammer pin is very easy to push out of recever when hammer is installedReplace hammer assembly
Inspect Remedy

Magazine Won’t lock in rifle

Inspect Remedy
Possible dirty or corroded magazine catch Disassemble and clean
Inspect for worn or broken magazine catch Replace magazine catch
Inspect for defecctive magazine catch spring Replace magazine catch spring

Rifle can not be zeroed

[Windage] determine if barrel assembly is out of alignment with rear sight on upper reciever Align barrel and upper receiver assembly
[Elevation] Inspect for defective front sight Remove front sight post, if damaged and Replace
[Elevation] Inspect for defective rear sight Repair as required
Inspect for defective or bent barrel assembly Replace barrel assembly

Selector Lever Binds

Dirt or sand under trigger Clean
Needs oil Lubricate

Short Stroking

Inspect for broken or bent gas tube Adjust or Replace gas tube
Carbon or dirt in carrier Clean
Inspect for carbon build up in barrel gas port Clean
Inspect for unlubricated or dirty action sprint and receiver extension Clean and lubricate
Inspect for carbon buildup in gas key Clean and lubricate
Inspect for broken or damaged action spring Replace action spring
Inspect for partially plugged gas system because of carbon buildup in gas tube Replace gas tube
Determine if roll pin is missing from gas block Replace roll pin
Inspect for improper gap space, worn missing or broken gas rings Stagger gas ring gaps, if worn broken or missing Replace gas rings and stagger gaps
Gaps in gas rings Stagger ring gaps
Questions

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  1. william asks Oct 7, 2019

    have a 308 ar with piston, works fine with steel cased monarch ammo but with brass cased ammo will at times fail to eject and double feed when chambering a single brass casted round with magazine our will stove pipe almost every time rifle has had about a 1000 rounds thru it, I keep it very clean, also notice steel cased ammo ejects forward and brass ammo will eject forward to the side and to the rear this is a sig 716 g2 ar rifle.

    1 people already voted for this question.

    1. Darren Peters answers Oct 8, 2019

      I imagine if you inspect the rim on your brass case ammo there is a deep gouge from the extractor. If your sig has an adjustable gas block try turning the gas down a hair with that ammo type or potentially a heavier buffer. Tough to troubleshoot over the internet but that's what I would check off the top of my head.

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  2. Dan G Farias asks Oct 10, 2019

    I am trying to use the reference to get the info without having to contact you with the question but i cant seem to narrow it down. I insert my mag, release the BCG forward, pull the trigger and fire a round, spent round ejects and loads next round, then it wont fire. 2nd round wont fire everytime. Right before incident i fired two 30rd mags. rifle is semi-atuo, no issue. Thank you.

    1. Darren Peters answers Oct 11, 2019

      This sounds like a trigger group related issue, sounds like the disconnector isn't working properly and maybe it chipped. When the rifle doesn't fire, can you pull the trigger again or is the trigger "dead" and won't release the hammer. If so, I'd try function testing it without an upper on it. Here is a great video of how the trigger is supposed to function. If yours isn't functioning like this, it is the problem.

      https://www.youtube.com/watch?v=bH6kQv65SuY&t=195s

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