AR went single shot for 8 rounds and I don't know why.

IMtheNRA · October 7, 2020, 08:44 PM

During a match last weekend, my carbine fired 8 consecutive rounds in single shot mode and I manually cycled the charging handle after each shot to eject the empty and chamber a new round. After those 8, it ran fine for the rest of the match. I fired about 80 rounds before the malfunction and about 120 after. Same handloads throughout the day.

I can't see anything broken, jammed, or out of order. The carbine is well oiled and it is not yet due for a cleaning.

Colt LE6920 with a JP trigger/hammer kit and JP buffer spring, Midwest Industries brake. Everything else is stock. About 8,000 rounds on the gun, about 5,000 rounds on the recoil spring.

All I can think of is the three gas ring gaps aligned with each other, but it seems like the odds of that happening are remote. And even if they did, would enough gas leak past them to stop the gun from completing the cycle?

Any idea what happened or what I should check next?

HiBC · October 7, 2020, 09:19 PM

I can't say for sure,but I would think if it was slightly short stroking it still would cock the hammer.

Did you detect hammer fall when you pulled the trigger?

That is the fork in the troubleshooting chart. If the hammer is dropping when you pull the trigger, its one set of potential problems. Not quite fully in battery,maybe.

If the hammer is not cocked when you pull the trigger,something about your trigger parts is not working correctly. You have an inertial firing pin.That means the hammer can ride the bolt carrier down without firing.

IMtheNRA · October 7, 2020, 09:25 PM

Good point. Yes, the hammer was cocked every time and I heard the click of the hammer when I pulled the trigger, so it was short stroking.

rickyrick · October 7, 2020, 09:54 PM

Sounds like something is loose, if it’s not mag related

stagpanther · October 8, 2020, 06:06 AM

I can't tell what actually happened from your description--are you saying you fired a shot and the spent case was left in the chamber, forcing you to manually cycle in order to eject the case and load a new cartridge?

imashooter · October 8, 2020, 07:27 AM

Check all gas from stem to stern.

9x19 · October 8, 2020, 07:47 AM

"...and I manually cycled the charging handle after each shot to eject the empty and chamber a new round."

"...the hammer was cocked every time and I heard the click of the hammer when I pulled the trigger..."

So, a failure to extract the spent case... but you didn't get a double feed, so bolt travel didn't pick up the next round in the magazine, but did cock the hammer?

Hmm, the failure to extract would lead me to check the extractor and tension (spring)... but it could also be something with those eight cases (didn't get FL resized when etc) that went wrong when reloading.

Skans · October 8, 2020, 08:18 AM

1. Check your gas block for alignment and any looseness.
2. Check your gas key on the bolt carrier.

If everything is tight and aligned, My guess would be there could have been some fouling in the barrel blocking the gas port, which finally broke loose from firing.

HiBC · October 8, 2020, 12:10 PM

Another key bit of information is needed.

When you cycled the action,did you eject a fired case,or a loaded round?

If a fired case,you have been given plenty of good advice regarding short stroking.

If you ejected a loaded round,it probably indicates your bolt as not 100% in battery.

If so,the hammer would lose its energy to the bolt carrier.
If this is the case,I'd look at your ammo. If your shoulder is not quite sized back enough it could cause this.

Metal god · October 8, 2020, 11:45 PM

It sounds to me like a cycling issue

your kidding

. No but really , now for the why ? First thought is ammo issues , why not "gas system" issues ? Cus it worked for 80rds , not for 8 then gtg for another 100+ . If the gas system it self was jacked , I'd expect more problems then 8 straight right in the middle of a large string . This is not to say it was not gas related , err wait WHAT ! I think something caused the ammo to be under powdered causing the short stroke and we are talking very short strokes .

These rounds were very under gassed to not even pull the case out of the chamber enough to cause problems in that aspect means the BCG moved very little . So I think it's a gas issue just not the gas system . There may have even been something stuck somewhere with in the gas system clogging it up and was blown out finally after the 8th round .

Another possibility could be something caused drag on the BCG slowing or preventing it from moving freely but I have no specifics of what those could be right off hand .

Anyways there's my $.02

Rondog · October 9, 2020, 01:06 AM

My AR did kinda the opposite one day. It went full retard on me, then just locked up and wouldn't work at all. The culprit turned out to be a fired primer that came out of a case and fell down into the trigger group.

T. O'Heir · October 9, 2020, 01:20 PM

"...due for a cleaning..." It should have been clean to begin with. Cleaning isn't a timed event.
Anyway, like Metal God says, it sounds like the gas system had some crud in it that cleared out by itself. Anything misplaces or damaged would not fix itself. A really good bath should fix anything that might be remaining.

rickyrick · October 9, 2020, 04:37 PM

I had a roll pin for the ejector back out and cause a similar issue once.

Bartholomew Roberts · October 9, 2020, 04:55 PM

They key question is were you ejecting an empty case or a live round?

Short-stroking isn’t unusual; but short-stroking where it cocks the hammer, doesn’t eject the empty, and doesn’t try to double-feed is an odd one. Odder still for the first 80 rounds to go OK, then 8 in a row bad, then works again.

If that’s what is happening, then I can tell you the rifle was trying to extract the case while residual pressure still had the case expanded against the chamber walls - and your extractor likely slipped off the rim (indicating a need to replace extractor spring/O-ring at a minimum). Why that happened and then corrected itself? A lot more questions needed to solve that puzzle.

What was the course of fire for the previous 80 rounds and latter portion where it worked again? Any downtime between those shoots?

Other helpful info - do you have any of the brass empties from that period? Bent/ripped rims?

ed308 · October 11, 2020, 09:44 AM

All I can think of is the three gas ring gaps aligned with each other, but it seems like the odds of that happening are remote. And even if they did, would enough gas leak past them to stop the gun from completing the cycle?

That's a myth. Even if all the three were aligned, it should still cycle. Additionally, since the gas rings move independently from each other, it's unlikely you'd have more that two aligned at any time. But I'd check them plus the rest of the gas system for wear based on your round count. Also, check the bolt tail and other areas for carbon buildup.

October 7, 2020, 08:44 PM	#1
IMtheNRA Senior Member Join Date: January 27, 2001 Posts: 298	AR went single shot for 8 rounds and I don't know why. During a match last weekend, my carbine fired 8 consecutive rounds in single shot mode and I manually cycled the charging handle after each shot to eject the empty and chamber a new round. After those 8, it ran fine for the rest of the match. I fired about 80 rounds before the malfunction and about 120 after. Same handloads throughout the day. I can't see anything broken, jammed, or out of order. The carbine is well oiled and it is not yet due for a cleaning. Colt LE6920 with a JP trigger/hammer kit and JP buffer spring, Midwest Industries brake. Everything else is stock. About 8,000 rounds on the gun, about 5,000 rounds on the recoil spring. All I can think of is the three gas ring gaps aligned with each other, but it seems like the odds of that happening are remote. And even if they did, would enough gas leak past them to stop the gun from completing the cycle? Any idea what happened or what I should check next?

October 8, 2020, 06:06 AM	#5
stagpanther Senior Member Join Date: March 2, 2014 Posts: 11,784	I can't tell what actually happened from your description--are you saying you fired a shot and the spent case was left in the chamber, forcing you to manually cycle in order to eject the case and load a new cartridge? __________________ "Everyone speaks gun."--Robert O'Neill *I am NOT an expert--I do not have any formal experience or certification in firearms use or testing; use any information I post at your own risk!*

October 8, 2020, 07:47 AM	#7
9x19 Senior Member Join Date: October 15, 1998 Location: Sherman, TX USA Posts: 3,750	"...and I manually cycled the charging handle after each shot to eject the empty and chamber a new round." "...the hammer was cocked every time and I heard the click of the hammer when I pulled the trigger..." So, a failure to extract the spent case... but you didn't get a double feed, so bolt travel didn't pick up the next round in the magazine, but did cock the hammer? Hmm, the failure to extract would lead me to check the extractor and tension (spring)... but it could also be something with those eight cases (didn't get FL resized when etc) that went wrong when reloading. __________________ Make mine lean, mean, and 9x19!

October 8, 2020, 11:45 PM	#10
Metal god Senior Member Join Date: April 10, 2012 Location: San Diego CA Posts: 6,876	It sounds to me like a cycling issue your kidding . No but really , now for the why ? First thought is ammo issues , why not "gas system" issues ? Cus it worked for 80rds , not for 8 then gtg for another 100+ . If the gas system it self was jacked , I'd expect more problems then 8 straight right in the middle of a large string . This is not to say it was not gas related , err wait WHAT ! I think something caused the ammo to be under powdered causing the short stroke and we are talking very short strokes . These rounds were very under gassed to not even pull the case out of the chamber enough to cause problems in that aspect means the BCG moved very little . So I think it's a gas issue just not the gas system . There may have even been something stuck somewhere with in the gas system clogging it up and was blown out finally after the 8th round . Another possibility could be something caused drag on the BCG slowing or preventing it from moving freely but I have no specifics of what those could be right off hand . Anyways there's my $.02 __________________ If Jesus had a gun , he'd probably still be alive ! I almost always write my posts regardless of content in a jovial manor and intent . If that's not how you took it , please try again . Last edited by Metal god; October 8, 2020 at 11:52 PM.

October 9, 2020, 01:20 PM	#12
T. O'Heir Senior Member Join Date: February 13, 2002 Location: Canada Posts: 12,453	"...due for a cleaning..." It should have been clean to begin with. Cleaning isn't a timed event. Anyway, like Metal God says, it sounds like the gas system had some crud in it that cleared out by itself. Anything misplaces or damaged would not fix itself. A really good bath should fix anything that might be remaining. __________________ Spelling and grammar count!

October 7, 2020, 09:19 PM	#2
HiBC Senior Member Join Date: November 13, 2006 Posts: 8,286	I can't say for sure,but I would think if it was slightly short stroking it still would cock the hammer. Did you detect hammer fall when you pulled the trigger? That is the fork in the troubleshooting chart. If the hammer is dropping when you pull the trigger, its one set of potential problems. Not quite fully in battery,maybe. If the hammer is not cocked when you pull the trigger,something about your trigger parts is not working correctly. You have an inertial firing pin.That means the hammer can ride the bolt carrier down without firing.

October 7, 2020, 09:25 PM	#3
IMtheNRA Senior Member Join Date: January 27, 2001 Posts: 298	Good point. Yes, the hammer was cocked every time and I heard the click of the hammer when I pulled the trigger, so it was short stroking.

October 7, 2020, 09:54 PM	#4
rickyrick Senior Member Join Date: March 15, 2010 Posts: 8,236	Sounds like something is loose, if it’s not mag related

October 8, 2020, 07:27 AM	#6
imashooter Senior Member Join Date: December 28, 2013 Location: Alabama Posts: 395	Check all gas from stem to stern.

October 8, 2020, 08:18 AM	#8
Skans Senior Member Join Date: November 20, 2008 Posts: 11,132	1. Check your gas block for alignment and any looseness. 2. Check your gas key on the bolt carrier. If everything is tight and aligned, My guess would be there could have been some fouling in the barrel blocking the gas port, which finally broke loose from firing.

October 8, 2020, 12:10 PM	#9
HiBC Senior Member Join Date: November 13, 2006 Posts: 8,286	Another key bit of information is needed. When you cycled the action,did you eject a fired case,or a loaded round? If a fired case,you have been given plenty of good advice regarding short stroking. If you ejected a loaded round,it probably indicates your bolt as not 100% in battery. If so,the hammer would lose its energy to the bolt carrier. If this is the case,I'd look at your ammo. If your shoulder is not quite sized back enough it could cause this.

October 9, 2020, 01:06 AM	#11
Rondog Member Join Date: March 15, 2009 Posts: 61	My AR did kinda the opposite one day. It went full retard on me, then just locked up and wouldn't work at all. The culprit turned out to be a fired primer that came out of a case and fell down into the trigger group.

October 9, 2020, 04:37 PM	#13
rickyrick Senior Member Join Date: March 15, 2010 Posts: 8,236	I had a roll pin for the ejector back out and cause a similar issue once.

October 9, 2020, 04:55 PM	#14
Bartholomew Roberts member Join Date: June 12, 2000 Location: Texas and Oklahoma area Posts: 8,462	They key question is were you ejecting an empty case or a live round? Short-stroking isn’t unusual; but short-stroking where it cocks the hammer, doesn’t eject the empty, and doesn’t try to double-feed is an odd one. Odder still for the first 80 rounds to go OK, then 8 in a row bad, then works again. If that’s what is happening, then I can tell you the rifle was trying to extract the case while residual pressure still had the case expanded against the chamber walls - and your extractor likely slipped off the rim (indicating a need to replace extractor spring/O-ring at a minimum). Why that happened and then corrected itself? A lot more questions needed to solve that puzzle. What was the course of fire for the previous 80 rounds and latter portion where it worked again? Any downtime between those shoots? Other helpful info - do you have any of the brass empties from that period? Bent/ripped rims?

October 11, 2020, 09:44 AM	#15
ed308 Senior Member Join Date: November 5, 2016 Location: DFW, TX Posts: 1,147	All I can think of is the three gas ring gaps aligned with each other, but it seems like the odds of that happening are remote. And even if they did, would enough gas leak past them to stop the gun from completing the cycle? That's a myth. Even if all the three were aligned, it should still cycle. Additionally, since the gas rings move independently from each other, it's unlikely you'd have more that two aligned at any time. But I'd check them plus the rest of the gas system for wear based on your round count. Also, check the bolt tail and other areas for carbon buildup.