AR-15 issues.

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bjaymz

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So I finally bought all the parts to assemble my ar. Got it all together and checked the headspace. First trip to the range was such a disappointment. I loaded a mag into the rifle and let the bolt go. When I pulled the trigger it went bang as I expected. However the spent casing was not extracted. The bolt came rearward an stripped another round from the mag and of course it jammed against the spent case in the chamber. I removed the mag and cleared the loaded round. Then I released the bolt and pulled it back to clear the empty and it ejected.
With the three remaining rounds in the mag I figured I would try it again. Same results. Cleared the same way. Everything seemed the same.
So I figured I would try the one remaining round in the mag. Inserted the mag, released the bolt and fired. Shot went off, extracted the spent case and fired it about 15’ to the right rear side as I was expecting the whole time. The bolt locked back into the rearward position.

I tried another mag with the same results.

I then switched the bcg in from another rifle and it fired like a champ.

It seems from looking at the brass that the extractor is slipping off the case rim. But why only with a loaded mag?

I figure it’s a bcg issue but my question is what part. I am new to the platform and I would like to know what the issue is. If anyone can think of anything, please let me know.
 
The most relevant thing to check is your Extractor Spring. Are you using the latest Spring with the Polymer Insert and Rubber O RIng? If not, then that is your culprit, guaranteed. If you do have the correct Spring System installed, the next thing to check is your Extractor itself. They are rarely faulty from the factory, but worth checking nonetheless. After that, my best guess would be over-gassing causing a too violent extraction cycle. Best of luck troubleshooting your problem!
 
x2 on the extractor. I can't explain why it only does it with a loaded mag though. These things are difficult to diagnose without having access to the rifle.
 
I installed the gas key. Bolt came pre assembled. I did disassemble it after the first range trip to ensure nothing was stuck/ not freely moving. There was a spring and washer present. Seems to have good tension. I am not sure what else to check as far as the extractor goes. When I rock a round in the bolt, bolt out of the rifle and in my hand, it seems to grab well. It extracts well with no rounds in the mag. And I assumed it was as the empty cases have a pretty good extractor scar.

Marc C what would cause overgassing?
 
Main reason is gas port is oversized for the port position. The bolt is unlocking prematurely. Getting a heavy buffer spring may help.

Do you have an adjustable gas block?

You did say your other BCG worked fine, correct? So I’m still inclined to think the problem is with components of the bolt. The extractor is the most likely culprit. You said you have a Nickel Teflon (boron?) BCG so maybe lubing isn’t the issue.
 
It is nickel boron.
I do not have an adjustable gas block but I may order one up.
If I was to get an adjustable block a heavier spring would not be needed I assume.
Thanks for the tips.
 
Barrel length?
Barrel brand? (some are known to be over-gassed more than normal)
Gas system length?
Carbine or rifle buffer tube?
If it's a carbine buffer what weight buffer?
Full auto or semi bolt carrier?

It sounds like you're over-gassed but hard to know without shooting the rifle or knowing what components it's built from.
When it cycles does the trigger reset itself hard? Enough you can feel it on your trigger finger every shot? I shot an AR before that was cycling so hard it would somehow force the trigger reset and hurt the trigger finger after a few shots, A heavier buffer settled it down enough that it cycled correctly at least even though it was still out of balance.

You need to balance the gas system to the recoil system if you want it to run smoothly, if your barrel gas port is too big you need to either add more weight and/or spring power to the recoil system or add an adjustable gas block to limit the amount of gas. I usually say that an adjustable gas block is a solution to a problem that doesn't exist as a rifle should not need one if the parts are compatible and in spec but these days the specs seem to wander around depending on brand.
 
OK, when you switched to a different bolt carrier group, the problem went away. That would suggest that the problem is with the original BCG.
You could try swapping bolts in the carriers. That might tell you if the problem is in the original bolt or in the original carrier.
You could even try swapping extractor assemblies.
 
bjaymz said:
16” barrel with carbine length gas.
Click to expand...

What brand is the barrel? Some are known to be over gassed more than others which would help to know so we can give better advice.

Like I said you need to have a balanced system, so your buffer weight and carrier design make a difference in how it runs. More info please or we're all just guessing.

Without more info I think Bartok has it in the over-gassing and premature unlock of the bolt causing your issues.

Since you have another BCG I'm guessing you have another AR? If so can you feel a difference when firing them? Does the new build kick more or feel not as smooth? You shouldn't feel the buffer slam into the back of the buffer tube (it will hit it but it shouldn't slam into it)?
 
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ok. I have a few things to try. I will get all the details of the build posted here later. I am gonna try the bolt from my other ar in the new carrier. I don’t recall any heavier recoil. But I will know for sure after tomorrow. Thanks for all the help. I know it’s hard to diagnose with the limited info I have mentioned. I will let you know how I make out at the range tomorrow trying the old bolt.
 
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Well fellas I went to the range this weekend. I swapped the bolt out with a spare another member had on hand. Everything ran great. That means the problem lies with the bolt and it’s components. I am quite convinced it is the extractor. I believe it is not fully seating on the case rim and is therefor slipping off instead of extracting. I thank all of you for your help on this.
True North Arms is where I bought the bcg and they have been excellent in making sure it’s right. Kuddos to them as well.
Cheers.
 
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