Weak extraction, failed to lock back

[tr1kstanc3]

I am experiencing some issues with weak extraction shooting Prvi M193 in a Stag Arms model 2 barrel. I have the following information to help troubleshoot.

1) Fails to lock back bolt on last round.
2) Tried both CAR and H buffer. Same issues.
3) Ejects around 2 o'clock.
4) Bolt has black insert and extra power extractor spring installed correctly.

Any ideas?

[5pins]

Sounds like week ammo or your gas key is loose. Check your gas key and try some other ammo.

[tr1kstanc3]

It's possible the ammo is weak but it is Prvi M193 so it should be of good quality. I tried another BCG and it has the same problem. The gas keys are staked properly.

[Redhat]

Try the ammo in another gun?

[RetreatHell]

Have you tried any ammo other than the prvi? I know it's good stuff and a little pricey (for my cheap ass), but it does happen.

Are you using a standard carbine buffer spring? Or are you running one of the extra strength ones that are a little longer to reduce muzzle flip and felt recoil?

It's not a rifle length spring is it? I know that sounds stupid, but it's happened.

That's really all I got for you, man. Me no armorer... me just shoot paper bad guys in face a lot:p

Semper Fi,

-Paul

[P2000]

Is it a new rifle?
If not, did it once work and now it doesn't work?
Does it lock back when cycling manually?

[ChicagoTex]

Sounds like you're undergassed, probably due to improper gas block installation. Who installed the gas block, Stag or you?

[C4IGrant]

Stag AR's are generally over gassed. PRVI ammo is usually pretty good.

Has the Stag ever ran correctly? The gas block could be off or the mags you are using are bad (weak springs).



C4

[az doug]

Weak extraction? It is extracting and ejecting but you feel it is not forceful enough? Why, because the bolt will not lock open after the last round? If that is the only indicator Grant may be correct regarding the magazines. Also it could be a broken or sticky "bolt release."

If you have symptoms other than the bolt not locking open, in addition to the other suggestions, you may also want to:

Check your chamber

Check for signs of gas leaking between the carrier and key (you will normally see it in the front right corner of the key, as you are looking from the back of the carrier)

Check for signs of gas leaking around the gas block

Check your rings

[99HMC4]

Is your rifle clean?

[tr1kstanc3]

Here is some additional information.

-I have used this ammo fine in another rifle.
-I tried 2 bolt carrier groups that are new. Both have same issues.
-Manually locking the bcg back works.
-Rifle is clean and lubed (running it wet).
-Using a standard carbine spring.
-Magazines are tested and working properly in other rifles.
-Rifle has less than 100 rounds through it. No FTE's or FTF's.

http://farm5.static.flickr.com/4035/4508113215_5b93d91d70.jpg

Is it possible the chamber is too tight and slowing down the BCG? This is my first time firing Prvi M193 5.56 from this particular barrel. I am going to go to the range on Monday to try out different ammo to see if its ammo related.

[P2000]

Sounds undergassed.

My guess would be the front sight block is not aligned with the hole in the barrel. Or there is a pretty significant gas leak. Less likely would be too strong of a buffer spring.

[Robb Jensen]

I am experiencing some issues with weak extraction shooting Prvi M193 in a Stag Arms model 2 barrel. I have the following information to help troubleshoot.

1) Fails to lock back bolt on last round.
2) Tried both CAR and H buffer. Same issues.
3) Ejects around 2 o'clock.
4) Bolt has black insert and extra power extractor spring installed correctly.

Any ideas?

I too think you likely have a lose carrier key. Stag does a poor job of carrier key staking and IMHO they don't torque the screws high enough.

Sounds like your extraction is good but ejection is weak. As long as the cases are making it our of the rifle I would worry about it much. Just be sure the ejector is lubed well.

What mags were you using?

[ForTehNguyen]

yea leaning towards gas system problem now.

My BCM middy with H buffer and BCM BCG shoots underpowered wolf all day long with no problems. I doubt it is ammo related, I never had a problem in any of my guns with Prvi M193. If my guns can eat wolf it can definately eat real stuff

[tr1kstanc3]

I too think you likely have a lose carrier key. Stag does a poor job of carrier key staking and IMHO they don't torque the screws high enough.

Sounds like your extraction is good but ejection is weak. As long as the cases are making it our of the rifle I would worry about it much. Just be sure the ejector is lubed well.

What mags were you using?

I switched out the carrier group with a BCM carrier group and experienced the same issue. The extraction is fine but the ejection is very weak. It kind of plops out of the rifle rather than being thrown out. I am using 20 round Pmags that work fine in other rifles.

[Thomas M-4]

I switched out the carrier group with a BCM carrier group and experienced the same issue. The extraction is fine but the ejection is very weak. It kind of plops out of the rifle rather than being thrown out. I am using 20 round Pmags that work fine in other rifles.\


I would check the chamber its possible it needs to reamed to a 5.56 chamber.

[Robb Jensen]

I switched out the carrier group with a BCM carrier group and experienced the same issue. The extraction is fine but the ejection is very weak. It kind of plops out of the rifle rather than being thrown out. I am using 20 round Pmags that work fine in other rifles.

Early Magpul 20 round PMAGs have trouble locking bolts to the rear when the rifle runs empty.

Does it lock to the rear with a 30 round PMAG?

It could just be the mags. If you have a 0-ring on your extractor remove it and the ejection force should throw the empties further. You only need the 0-ring on CAR length gas guns.

[tr1kstanc3]

Early Magpul 20 round PMAGs have trouble locking bolts to the rear when the rifle runs empty.

Does it lock to the rear with a 30 round PMAG?

It could just be the mags. If you have a 0-ring on your extractor remove it and the ejection force should throw the empties further. You only need the 0-ring on CAR length gas guns.

I have not tried with a 30 round pmag. I will test that on Monday along with different ammo.

I do not have the O-ring installed. I am using only the black insert with spring kit that BCM offers.

[tr1kstanc3]

\


I would check the chamber its possible it needs to reamed to a 5.56 chamber.

I am suspicious about this being the issue as well.

[C4IGrant]

I have not tried with a 30 round pmag. I will test that on Monday along with different ammo.

I do not have the O-ring installed. I am using only the black insert with spring kit that BCM offers.

That extraction setup is just fine.


C4

[Iraqgunz]

Let me throw in my 250 afghanis worth. My guess is there is something wrong with the gas port. Have you contacted Stag? I would maybe consider replacing the gas tube.

[ForTehNguyen]

if the chamber was too tight, wouldnt you feel resistance if you charged it manual. If so that would be a dead giveaway

[Redhat]

If everything else is good to go and other possibilities have been eliminated, I wouldn't change anything. I'd call Stag to fix it.

[tr1kstanc3]

I'm going to troubleshoot first myself before contacting Stag primarily to learn for myself. Thanks for the input everyone. Will report back after my range trip Monday to test some ideas given here.

[Iraqgunz]

Not necessarily. All of our Bushamsters were tight and malfunctioned with certain types of 5.56 ammo. But almost never with Lake City.


if the chamber was too tight, wouldnt you feel resistance if you charged it manual. If so that would be a dead giveaway

[Robb Jensen]

I'm going to troubleshoot first myself before contacting Stag primarily to learn for myself. Thanks for the input everyone. Will report back after my range trip Monday to test some ideas given here.

FWIW my thoughts:

I think there's a 70% chance it's the 20 round PMAGs and 20% chance it's a leaking carrier key and a 10% it's a combination of the two....

If it were mine I'd ream it with a 5.56mm neck and throat reamer if it failed the test with the 5.56mm neck and throat checker. All Stags (about 90 barrels) I've ever dropped this checker into made it stick...this means they're on the tight side for 5.56mm NATO in the neck and throat area of the chamber. The checker and reamer are available from Ned Christiansen. I'd also replace the Stag carrier key with a BCM carrier key and new 158 grade Carpenter steel bolts. I use TorX bolts from Fastenal myself and then stake with a MOACKS.

[fike]

FWIW my thoughts:

I think there's a 70% chance it's the 20 round PMAGs and 20% chance it's a leaking carrier key and a 10% it's a combination of the two....

If it were mine I'd ream it with a 5.56mm neck and throat reamer if it failed the test with the 5.56mm neck and throat checker. All Stags (about 90 barrels) I've ever dropped this checker into made it stick...this means they're on the tight side for 5.56mm NATO in the neck and throat area of the chamber. The checker and reamer are available from Ned Christiansen. I'd also replace the Stag carrier key with a BCM carrier key and new 158 grade Carpenter steel bolts. I use TorX bolts from Fastenal myself and then stake with a MOACKS.

I was having issues today with my new SR-15 lower not locking back after the last round when using a 20 round PMAG. I switched to a 30 round PMAG and never had an issue the rest of the day.

[ADCTD2SHOOTING]

Just a few suggestions, first look at the fired brass and see if the rim is bent badly possible indication of a tight chamber (of course a chamber gauge is the best way to test this). If the chamber is good and there are no gas leaks that you can find and before you try to pull the fsb to check gas port, seperate the upper and lower and press up on the bolt carrier group with your finger (to simulated rounds in a loaded mag pushing) while pulling the bolt carrier rearward with your other hand (you are looking to find if there is any drag between the bolt lugs and the barrel extension) if the carrier assy, upper or barrel extension are out of spec or the tolerances stack badly it can cause problems and it will hang up.

I have only seen this once before myself (of course it was my rifle) and it had me tearing whats left of my hair out. In my case the upper and barrel ex were fine and it was the bolt carrier that was the culprit and the manufacturer replaced it without problem and apoligized for my frustration.

Just to make sure there is no misunderstanding none of the parts I had were stag or bcm so I'm not saying anything about those brands. But it is now one of the first things I check out on an ar.

Hopefully this isnt your problem and it is easily fixed, just sharing my bad (parts) experience however it was a very good customer service experience with the manufacturers of my parts.

[tank254]

I was having issues today with my new SR-15 lower not locking back after the last round when using a 20 round PMAG. I switched to a 30 round PMAG and never had an issue the rest of the day.


Same with my Noveske Crusader/LMT Defender lower (H2 buffer) running XM193.

It locked back fine on all of my various 30rd mags, but nearly always failed to lock back on the one 20rd Pmag that I was using. There were otherwise no other failures of any kind and the ejection pattern seemed perfect.

HTH

[tr1kstanc3]

Here's an update on the status of the rifle after taking it to the range today.

(using Federal .223 bulk pack)

-Tried USGI 20 round and Pmag 30 round mags and both locked back successfully.
-20 round Pmags periodically locked back.
-Ejection was strong and cases were flung out a few feet rather than plopping out a few inches from the rifle compared to the Prvi M193 ammo.
-Gas key/gas tube do not appear to be an issue.

I did not fire any Prvi today. I think the problem I am having is a tight chamber with the 5.56 rounds. If I were to get the chamber reamed, how much does this affect the accuracy of the barrel?

[jmart]

Here's an update on the status of the rifle after taking it to the range today.

(using Federal .223 bulk pack)

-Tried USGI 20 round and Pmag 30 round mags and both locked back successfully.
-20 round Pmags periodically locked back.
-Ejection was strong and cases were flung out a few feet rather than plopping out a few inches from the rifle compared to the Prvi M193 ammo.
-Gas key/gas tube do not appear to be an issue.

I did not fire any Prvi today. I think the problem I am having is a tight chamber with the 5.56 rounds. If I were to get the chamber reamed, how much does this affect the accuracy of the barrel?

What leads you to this conclusion?

[Iraqgunz]

Just a little FYI on the Prvi Partizan. We had issues with this ammo when I was in Iraq (2007-2009). The ammo in question was 5.56 SS109 made in 2004 or so. The weapons were Bushamster carbines.

We experienced multiple failures to extract and popped primers in every magazine we shot. Once we reamed the chamber with Ned Christiansens reamer we we experienced a huge decrease in issues. We never had problems with the Lake City M855 or M193 ammo we had.

So what was the actual cause? Not sure. I think it was a combination of the tight chambers and the ammo. We experienced the same type of issues with lots of Bulgarian SS109 ammo that we purchased as well.

The LMT and Colt uppered weapons that I slapped together experienced almost no issues at all with the ammo.

[ForTehNguyen]

Prvi should be good, I've used them without issue in my BCM and Delton uppers

[hammonje]

My Stag model 1 had very similar issues. It would not lock back using USGI Vietnam Era USGI magazines (Simmons, Advetureline, Colt) and the ejection was terrifically weak.

I solved the problem with the BCM extraction spring and an H buffer since the bolt was catching the case before it was ejected. Problem solved except that the ejection is still quite weak. It functions 100% of the time now though. Still will not keep the bolt locked back on an empty USGI Vietnam Era 20-round mag.