AR 15 not picking up the next round

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dennism

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Started discussing this on the Boise BCG Group buy but may get some more results here. My recent AR build is not picking up the next round when it fires. I tried my rifle with another known to be working BCG and it worked perfectly. Would this rule out the gas system/upper being the cause of the problem?

Any trouble shooting advice would be appreciated this is my first AR so not sure on the best method of adjusting.
 
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dennism said:
I tried it my rifle with another known to be working BCG and it worked perfectly.
Click to expand...

well "it" may not be the problem, whatever it is

so does it load okay from the bolt lock back position?

does it lock back on the last round--put one round in the mag and fire?

try different magazines?

what components? could be under-gassed: not getting enough gas blown into the BCG. or it just might need a little oil
 
dennism said:
Started discussing this on the Boise BCG Group buy but may get some more results here. My recent AR build is not picking up the next round when it fires. I tried it my rifle with another known to be working BCG and it worked perfectly. Would this rule out the gas system/upper being the cause of the problem?

Any trouble shooting advice would be appreciated this is my first AR so not sure on the best method of adjusting.
Click to expand...

The FA BCG has more meat on it so it runs differently than the Semi one. Most likely a recoil related issue. The buffer, spring and BCG need to work in harmony with the gas system and the particular load. If you have a really big spring and buffer it would take more pressure to push the BCG to the rear and vise versa. The good news is its not rocket science and you can take out your spring, buffer, and bolt and put it on the table next to one from a well running AR and most likely figure it out.
 
Sorry about that subtract the "it" and the sentence makes sense. Rifle does not lock back on an empty mag. Tried the rifle with one of the range masters known to be operating 10 rounders with no luck. Tried the rifle with one of his H3 buffers and buffer spring with no luck. Switched in his BCG and the rifle functioned. Went back to my buffer/spring and mag and his BCG still worked. The rifle has a troy low profile gas block and mid length gas system. Barrel is a 16" BCM Middy. My buffer tube is a BCM mil spec tube with a standard carbine buffer. http://www.bravocompanyusa.com/M4-Stock-Milspec-p/stock m4 milspec black - gen2.htm
 
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dennism said:
Sorry about that subtract the "it" and the sentence makes sense. It does not lock back on an empty mag. Tried the rifle with one of the range masters known to be operating 10 rounders with no luck. Tried the rifle with one of his H3 buffers and buffer spring with no luck. Switched in his BCG and the rifle functioned. Went back to my buffer/spring and mag and his BCG still worked. The rifle has a troy low profile gas block and mid length gas system. Barrel is a 16" BCM Middy.
Click to expand...

The bolt could be out of spec but it would have to be WAY out of spec to totally miss the round you would be able to see it with the naked eye. Also, check the 3 rings in your bolt and make sure the cracks are not all lined up you may be "passing gas".
 
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The range master took a look at the rings and confirmed they were properly aligned. The BCG does move freely when I charge the rifle.
 
Mike-Mike said:
The bolt could be out of spec but it would have to be WAY out of spec to totally miss the round you would be able to see it with the naked eye. Also, check the 3 rings in your bolt and make sure the cracks are not all lined up you may be "passing gas".
Click to expand...

the three ring alignment thing is a MYTH. MYTH. MYTH. Yes, it's in an old Army instruction book somewhere but you can run a properly built AR with just ONE gas ring. We did it at the Armalite course just to bust that myth.

but yeah, it could be that this carrier has more mass? are you using a standard weigh buffer?

check for leaks on the BCG:

Gas Key Leakage - AR15.Com Archive

did you swap the entire BCG with bolt and all? might be a headspace issue, could try swapping bolts
 
I have not tried swapping the bolts yet. If i manage to get to the range today I will both try the two different assemblies and swap the bolts in the assemblies. Thanks for the link on the leakage. Will check that out. Standard weight buffer, but was also tried with an H3 buffer with no change in results.
 
There really is not enough information other than to offer various suggestions. Ammo, feed ramp info, and difference between one BCG v other BCG .... could be as simple as the ammo ..
 
What's the rest of your upper combo (barrel, gas system, etc...)? What kind of ammo were you using, was it brass or steel?

I had some fail to feed / fail to eject issues with my Boise BCG build, then ultimately got a case stuck in the barrel. I ultimately attributed it to steel ammo, and a build that wasn't broken in yet... here's my thread for reference:

http://www.northeastshooters.com/vbulletin/build-yourself/217392-ar-bolt-carrier-stuck.html

I've since cycled another ~100 or so rounds of brass through without issue.

Edit: I've got some headspace gauges if you want to check that... I could meet you up at Holbrook Sportsmen's if that's close.
 
turbo89 said:
What's the rest of your upper combo (barrel, gas system, etc...)? What kind of ammo were you using, was it brass or steel?

I had some fail to feed / fail to eject issues with my Boise BCG build, then ultimately got a case stuck in the barrel. I ultimately attributed it to steel ammo, and a build that wasn't broken in yet... here's my thread for reference:

http://www.northeastshooters.com/vbulletin/build-yourself/217392-ar-bolt-carrier-stuck.html

I've since cycled another ~100 or so rounds of brass through without issue.

Edit: I've got some headspace gauges if you want to check that... I could meet you up at Holbrook Sportsmen's if that's close.
Click to expand...

Barrel is a BCM 16 inch standard middy, Aero precision upper both have M4 feed ramps. Gas block is a Troy low profile. Used tula ammo initially but the range master tried to cycle some of his brass (PMC) I think with no change in results only success was with his BCG. I have had the rifle headspaced by 1776 gunsmithing when they were pinning my muzzle device and it came back OK.
 
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Is it failing to eject, then not picking up the next round, or is it ejecting fine and then not picking up the next round? Any pictures of the failure(s)?

How was it lubed, was it running dry?
 
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It was ejecting most of the rounds fired but not picking up the next round. It was somewhat dry at first but lubed it up after the first few failures to no effect. No picture of the failure yet will try and get one.
 
Pictures of the failure and some of the feedramp / BCG would help trying to troubleshoot. Here's a troubleshooting guide I found on the High Road:

Zero bolt movement when round discharges:

Missing gas tube roll pin
Upside down gas tube
Missing or broken buffer tube retainer
Obstruction in buffer tube

Bolt short cycles when shot:

Leaking gas key
Bad gas rings
Leaking gas block
Recoil spring is too strong
Wrong type of buffer installed
Too many rounds in the magazine
Action is not oiled enough
Gas tube roll pin is missing
Gas block is not properly oriented
Carbon buildup causing sluggish movement
Bad ammunition

Rifle does not feed right when shot:

Too many rounds in the magazine
Magazine is not properly seated in lower
Weak magazine spring
Rifle may not have M-4 feed ramps
Check for home gunsmithing of feed ramps


Rifle does not lock open after last round:

Weak magazine spring
Damaged follower
Bad ammunition (low pressure= cycle failure)
Magazine is not fully seated
Damaged bolt catch
Carbon buildup around bolt catch


Rifle does not fire when trigger is pulled (Click but no bang):

Broken firing pin tip
Carbon on back of firing pin = less protrusion
Weak hammer spring
Excessive headspace
Bad ammunition (faulty primer)
Missing firing pin
Bolt is out of battery (check for bolt bounce)


Rifle double fires or string fires:

Improperly adjusted adjustable trigger
Worn out military trigger
Home gunsmithing stoning job
Missing trigger spring
Missing or worn disconnector
Carbon build up on firing pin


Round is jammed under charging handle:

Worn magazine feed lips
Worn magazine spring


Rifle double feeds when shot:

Bad magazine
Broken extractor
Worn extractor spring
Carbon in chamber


Trigger won’t move when pulled:

Obstruction underneath (primer or rock)
Safety selector is engaged
Bolt is locked open

Round doesn’t extract when shot:

Broken extractor
Worn extractor spring
Dirty or corroded ammunition
Case head separation
Carbon in chamber
Lacquer coated ammunition


Round does not fully chamber:

Dirty or corroded ammunition
Improperly sized reloads
Tight headspace (check proper bolt fit)
Carbon in chamber

Bullets keyholing on target:

Improper bullet weight to rifle twist ratio
Check for rifling in barrel

Magazine inadvertently drops out of rifle:

Improperly seated magazine
Broken or faulty magazine catch
Ambidextrous magazine catch
Worn out polymer magazine
Bargain quality polymer magazine

Extractor breaks frequently:

Discontinue use of steel case ammunition

Bolt is frozen half way back:

Buffer is lodged in buffer tube
Check for rough machining of buffer tube

Rifle won’t hit broad side of barn:

Optic is not properly sighted in
Poor quality ammunition
Check for proper ammunition caliber
Operator error, contact local instructor for training

AR-15 Failure to feed issues - THR
 
Is the gas key tight on the carrier?
As somebody said before, is she properly lubed?
With the bolt carrier assembly removed, push the bolt into the carrier, and hold the carrier by the opposite end, and flick it like your cracking a whip, does the bolt move and lock forward?
 
This one sounds stupid simple, but look at the mag release button.
Is the end of the threaded rod flush to the face of the button?
If it's not, push it in far enough with a dowel or something plastic to avoid scratching, so the flat portion on the opposite side comes out far enough to turn it.
Turn it in just one rotation clockwise and release the button back into place.
Sometimes a failure to strip the next round off the mag ,is the mag catch isn't fully engaged and the mag is sitting a hair too low.
 
Tore the upper apart to check on the gas block. Was in proper place tho. Tightened my barrel nut a bit more to try and straighten out the gas tube. Going to manually cycle it a bit tonight and see if I get anywhere.
 
if you had the upper apart you can blow test the gas system. you can still do this with the upper off: spray some soapy water around the gas block, block the chamber with a finger, block the gas tube with another finger and blow down the barrel. look for leaks--bubbles--and note if you feel resistance as you blow. try and hum yankee doodle dandy as you blow--that's an important part of the test.

doesn't sound like a gas tube mis-alignment, that usually causes a failure to feed: next round gets pushed towards the chamber but doesn't go into battery completely

did you leak check the BCG yet? that's my #1 suspect.

if you do swap out bolts at the range, look at the brass ejected. is it warped or distorted? does it eject and bounce forward 15 ft? or does it eject to the rear just a couple feet?
 
dennism said:
Tore the upper apart to check on the gas block. Was in proper place tho. Tightened my barrel nut a bit more to try and straighten out the gas tube. Going to manually cycle it a bit tonight and see if I get anywhere.
Click to expand...

You didn't clean the gas key with a qtip did you? Check the gas key for obstructions. Take the bolt out of the BCG and push the carrier into the upper checking for proper gas key/gas tube alignment. Check BCG 1 vs. BCG 2 for any dissimilarity.
 
Another_David said:
if you had the upper apart you can blow test the gas system. you can still do this with the upper off: spray some soapy water around the gas block, block the chamber with a finger, block the gas tube with another finger and blow down the barrel. look for leaks--bubbles--and note if you feel resistance as you blow. try and hum yankee doodle dandy as you blow--that's an important part of the test.

doesn't sound like a gas tube mis-alignment, that usually causes a failure to feed: next round gets pushed towards the chamber but doesn't go into battery completely

did you leak check the BCG yet? that's my #1 suspect.

if you do swap out bolts at the range, look at the brass ejected. is it warped or distorted? does it eject and bounce forward 15 ft? or does it eject to the rear just a couple feet?
Click to expand...

Haven't gotten to the range yet am going to try and make it out tomorrow. Will also test the BCG for leaks. WIll also report back on the condition of the brass, will take a picture.
 
Finally got to the range. Could not get either bolts to cycle. Adjusted the gas tube to make sure it went in perfectly straight before hand. Going to swap the uppers. I had to drill out the hole for the front lower pin hole on the upper to go through so maybe the rest of the upper is out of spec too. Grabbed the brass(steel) will take a pic of it tonight.
 
I suspect I have solved it. I think I had the hammer spring installed backwards, I spun it around and the ar is much easier to charge and the bolt seems to be operating much more smoothly.
 
Hopefully you have solved it. Every time I have fired an AR or an FAL they had no FTE or FTF's. I did have some FTE's on my Marlin, but I think that was due to weak ammo. My bigger 'toys' have not had either a FTE nor a FTF. Even my 7.62x54R generally behaves itself.
 
If I get to the range tomorrow (unlikely) I will update. Thanks for the help guys, I am crossing my fingers. 2013-10-18 21.03.59.jpg
 

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I have the upper same parts as you ... BCM mid length 16" barrel , A BCM low profile gas block and I think I bought the BCM gas tube , Areo Matrix upper , except I have a BCM BCG and was running a similar issue? ... It fails to lock back after the last round is fired and ejected , fired 5 rds in a row with no issue . This AR was built by myself. I only tired it with a Bushmaster 10 rd mag I purchased that day so I was Ma. compliant with my free state complaint AR .

I'll check my Mag catch button as suggested above and hope to get to the range to try the H Buffer and a carbine buffer i bought, I was running a Spikes T2 buffer. In the case of the OP switching from a carbine buffer to an H3 would have been the wrong thing to do if I've read up on this issue correctly???
 
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