308 cycling issues (pics of brass)

Thejeff1987

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Nov 5, 2018
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#1
The rifle is a new build, aero receiver set, Wilson combat barrel, seekins adjustable gas block. If someone needs more info than that I can provide

Here’s the deal, when under gassed, the gun won’t extract the spent casing, gas block opened all the way and it ejects the case but won’t cycle the next round. Moving in 1/4 turn increments the rifle will not cycle, and fails to lock back when firing the last round also.

Initially I thought gas issue, and spent a significant amount of time playing with it to no success, yesterday I noticed the brass was receiving in’s interesting treatment. As indicated in the attached photos, there are two rake marks and the neck is slightly dented. This is the situation on all the brass regardless of whether the rifle ejected it, or if I had to mortar the case out.

After noticing the brass, I inspected the upper/chamber and there were brass shavings there from whatever is scraping the brass on the way out.

Any help on where to start on this diagnosis/fix is appreciated
 

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TMR137

Full Member
Feb 16, 2017
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#2
I see the same brass marks on many of my and my friends semi autos. The marks on the neck are from the round being chambered and dragging on your feed ramps. The slight dent on top is more than likely from it hitting your brass deflecter.

If you are comfortable with it you can polish the edges of your feed ramps and that will help your neck scratches.

If you are not getting bolt lock back on last round with full open gas block,my questions would be what Buffer and spring weights are you using and have you checked different magazines to ensure that isn’t the issue. I would also wonder about your ammo, is it factory or hand loads, light, heavy, etc. your round might just not have enough pressure to lock the bolt back.
 
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Thejeff1987

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Nov 5, 2018
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#3
The dent isn’t from the deflector because the rounds I have to mortar out of the gun that do not hit the deflector have them also which was interesting to me Because that’s what I thought too.

My next thought was buffer issue. Running AR stoner buffer tube kit (midway part 335126) for lr-308, I was thinking that’s the next place to look in the chain of events.

Hand loads and multiple different factory ammunition at varying velocities, all pretty much same results.
 

TMR137

Full Member
Feb 16, 2017
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#4
What BCG are you running and did you have the bolt head spaced to the barrel? I run a WC barrel on one of mine and they told me that not all “DPMS” pattern bolts run with their barrels.
 

TMR137

Full Member
Feb 16, 2017
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#6
Ok. That’s the same BCG I have with my WC barrel. So it should work just fine. How many rounds do you have through the BCG and barrel combo? Can you see any scaring or marring on the inside of the buffer tube or on the buffer retaining detent? I haven’t used the AR-Stoner tubes but I have had others where I had to sand down the coating on the inside as it was to thick and not consistent. Another thing to check would be the alignment of your gas block, any chance it may be off set?
 

BCP

Lt. Colonel
Dec 4, 2008
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#9
TBH if you are having to pogo it to get brass out you probably didn't headspace it properly. You did check it before you put it together...right? If not then a quick/dirty method is to tear apart the upper, take the bolt out of the carrier and then with the bolt in one hand/barrel in the other try to hand chamber a new/resized piece of brass.

Gas port alignment is easy, you just loosen the gas block and look at the gas port hole. You'll see a carbon ring around it from the hole in the gas block that gas flows through. The carbon ring should be more or less centered around the gas port hole.
 

Thejeff1987

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Nov 5, 2018
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#10
TBH if you are having to pogo it to get brass out you probably didn't headspace it properly. You did check it before you put it together...right? If not then a quick/dirty method is to tear apart the upper, take the bolt out of the carrier and then with the bolt in one hand/barrel in the other try to hand chamber a new/resized piece of brass.

Gas port alignment is easy, you just loosen the gas block and look at the gas port hole. You'll see a carbon ring around it from the hole in the gas block that gas flows through. The carbon ring should be more or less centered around the gas port hole.
Headspace no problem on go/no go gauges.
Here’s a picture of the gas port

Let’s keep hearing thoughts.
Tore the entire firearm down so I can inspect anything and provide whatever info needed.
Is it possible the buffer/spring are an issue?
 

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hlee

Sergeant
Jul 14, 2012
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#11
If you are mortaring the rifle to get the shell to extract, it is as likely as not that it is ejecting with sufficient force to hit the shell deflector and get dented. If you drop an empty case on a concrete floor, the mouth can deform like that. It doesn't take much.

The scratches can be caused by the spent shell scraping along the locking lugs in the barrel extension.

With the gas full open, does the rifle lock back on an empty magazine? If so, your bolt speed (when full open) may be so fast that the magazine cannot push a round up fast enough to get stripped from the mag by the bolt.

Does your gas block have detents on the adjustment screw? How much latitude do you have in the adjustment? Can you go 1/8 turn, 1/16 turn?

If you are going from too fast to strip a round at full open to not extracting with a single 1/4 turn, you might try a different magazine with a stiffer spring. But, if the rifle is not locking back on an empty magazine at full open, you have a different issue.
 

Thejeff1987

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Nov 5, 2018
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#12
If you are mortaring the rifle to get the shell to extract, it is as likely as not that it is ejecting with sufficient force to hit the shell deflector and get dented. If you drop an empty case on a concrete floor, the mouth can deform like that. It doesn't take much.

The scratches can be caused by the spent shell scraping along the locking lugs in the barrel extension.

With the gas full open, does the rifle lock back on an empty magazine? If so, your bolt speed (when full open) may be so fast that the magazine cannot push a round up fast enough to get stripped from the mag by the bolt.

Does your gas block have detents on the adjustment screw? How much latitude do you have in the adjustment? Can you go 1/8 turn, 1/16 turn?

If you are going from too fast to strip a round at full open to not extracting with a single 1/4 turn, you might try a different magazine with a stiffer spring. But, if the rifle is not locking back on an empty magazine at full open, you have a different issue.
Rifle only occasionally locks back on empty mag. The range of the gas block is 4.5 full turns to be all the way open. I have on multiple occasions started at full open and worked back in half turns. Random at best when it locks back and or feeds. At 75-80 open I can get the rifle the eject a case, but not strip the next round in. Anything less gassed then that and I have to mortar it out.
 

hlee

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Jul 14, 2012
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#13
Sounds undergassed. Who made the barrel? Any way to measure the gas port size? Have you inspected the bolt carrier group? Any indication it may be dragging? What are the chances you have a rifle recoil spring in a carbine extension?
 

Thejeff1987

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Nov 5, 2018
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#14
Sounds undergassed. Who made the barrel? Any way to measure the gas port size? Have you inspected the bolt carrier group? Any indication it may be dragging? What are the chances you have a rifle recoil spring in a carbine extension?
Wilson combat barrel, bcg is disassembled and no signs of dragging. Standby while I review parts sheet to confirm extension and spring parts
 

BCP

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Dec 4, 2008
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#16
gas port is slightly misaligned but not bad.

maybe I"m confused, is it hard to extract fired brass? Do you have to really bang on the charging handle to get it out?
 

Thejeff1987

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Nov 5, 2018
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#17
gas port is slightly misaligned but not bad.

maybe I"m confused, is it hard to extract fired brass? Do you have to really bang on the charging handle to get it out?
Not super hard, just don’t want to pull on the charging handle that hard so I give it a light pogo
 

whatsupdoc

Duck season
Dec 12, 2017
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#18
Can the bolt carrier be pulled back manually and lock?
Is the buffer spring correct length, just because it all came in a package does not mean anything.
Is the gas block really fully open?
Do you see any signs of gas leakage around gas block?
Is the bolt carrier key tight?
Are the bolt gas seals good?
Any dents in the gas tube?
Does the carrier move in and out of battery without any binding?


Nothing else I can think of.
 

Thejeff1987

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Nov 5, 2018
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#19
Here’s a question as I’m going back over everything... what are the differences in carbine and rifle buffer tubes and their respective buffers and springs. Doing some research, some I may have a carbine tube/buffer/spring. Would changing to rifle length be a possible situation to solve the issue?
 

Mike_in_FL

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Feb 29, 2008
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#20
What would be my indicator the gas block isn’t lined up, it’s a seekins adjustable, and the barrel has a notch for one of the two screws to orient it?
Just because one of the screws lined up doesn't mean anything. SLR, I think, sells a kit to drill the indents. The kit aligns to the gas port because the center to center distance can be like, either .400" or .450" between the screws. I would either buy one of the plastic gas port alignment kits or measure the distance on the barrel to the port and then the distance from the rear edge of the Seekins AGB to its port.

I'm becoming the spokesperson for the Every Day Sniper podcast. The guys from Mile High were talking about how they build gas guns and they use a borescope to ensure the gas port on the barrel is perfectly lined up with the gas block.


 
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Mike_in_FL

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Feb 29, 2008
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#21
Here’s a question as I’m going back over everything... what are the differences in carbine and rifle buffer tubes and their respective buffers and springs. Doing some research, some I may have a carbine tube/buffer/spring. Would changing to rifle length be a possible situation to solve the issue?
The spring and buffer you show is meant to be used with a 6 position mil-spec carbine receiver extension or buffer tube. You don't have enough gas it sounds like.
 

Thejeff1987

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Nov 5, 2018
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#22
The spring and buffer you show is meant to be used with a 6 position mil-spec carbine receiver extension or buffer tube. You don't have enough gas it sounds like.
It’s all one package, carbine length tube, carbine buffer and spring. My question was asking if going to a rifle tube, buffer, and spring would make a difference
 

Mike_in_FL

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Feb 29, 2008
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#23
It’s all one package, carbine length tube, carbine buffer and spring. My question was asking if going to a rifle tube, buffer, and spring would make a difference
And I'm trying to not spoon feed you answers after I gave you a couple of videos to look at. If you're going to build ARs, learn how to troubleshoot them. What makes the BCG retract and eject cases? What doesn't yours do the majority of the time?

Do YOU think changing buffers matters at this point?

You didn't answer many of the questions people asked you trying to diagnose your problem for free before I responded. If there isn't some kind of mechanical binding that prevents using the CH to pull the BCG back and lock open on an empty magazine, then NO changing buffers isn't going to do squat at this time.
 

Thejeff1987

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Nov 5, 2018
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#24
And I'm trying to not spoon feed you answers after I gave you a couple of videos to look at. If you're going to build ARs, learn how to troubleshoot them. What makes the BCG retract and eject cases? What doesn't yours do the majority of the time?

Do YOU think changing buffers matters at this point?

You didn't answer many of the questions people asked you trying to diagnose your problem for free before I responded. If there isn't some kind of mechanical binding that prevents using the CH to pull the BCG back and lock open on an empty magazine, then NO changing buffers isn't going to do squat at this time.
I suppose I should have answered them on here, however I did answer them for myself. I did watch the videos you sent.
After inspecting the chamber of the barrel (since eliminating all the other possible solutions that were brought up) it looks extremely rough. I hadn’t considered that as an option initially given the manufacture. The firearm cycles correctly after polishing the chamber and removing significant tooling and burrs.

Thanks to everyone for the help
👍
 
Aug 7, 2017
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#25
I am not the OP but I do have a question about the denting and scratching of the neck of the case. I have a DPMS LR 308 and I am curious if there is anything that can be done to keep the locking lugs from gouging or scratching and denting the necks of the spend cases? I would love to make my brass last a couple more reloads but it seems like the marks in the neck are worse than the pictures that the OP posted. I can’t post a picture right now but I can this evening.