What's the cause of this?

Gatehouse said:
Thousands of rounds with no problem, now a stovepipe per 10 rounds. Gun is clean. I pulled the BCG and swapped it with another rifle. Didn't fix the problem and the other rifle works fine so it's not BCG related I don't think.

Buffer spring worn out? Gas tube not letting enough gas through?

https://www.facebook.com/video.php?v=10156423410920516
Click to expand...

Can't see pictures.

Does the bolt lock up on an empty mag?
does it extract properly but fail to pick up a round?

Way too little info, but my first instinct is gas. If its not the rings in the BCG, seems you ruled that out, then it could be the gas tube. Buffer springs should be easy enough to swap if you have access to another. Tubes are only slightly more work. The first time you buy spare rings or tubes, buy a bunch. Shipping costs more than the parts.
 
Gatehouse said:
Thousands of rounds with no problem, now a stovepipe per 10 rounds. Gun is clean. I pulled the BCG and swapped it with another rifle. Didn't fix the problem and the other rifle works fine so it's not BCG related I don't think.

Buffer spring worn out? Gas tube not letting enough gas through?

https://www.facebook.com/video.php?v=10156423410920516
Click to expand...

Well the link is broken so there's that. Gas tube bcg buffer spring. Got some pipe cleaners?
 
Have the same problem. In my case, it is the magazine. The follower is not in the right position and it changes the angle of the last round as it is being extracted.
 
Garaldtao said:
Have the same problem. In my case, it is the magazine. The follower is not in the right position and it changes the angle of the last round as it is being extracted.
Click to expand...

I thought it was magazine at first too, but I have tried about a dozen mags and most of them have the same problem, yet in the other 2 rifles the mags work fine. Most of the time it's the 3rd to last round that doesn't eject properly though.
 
Generally looks like ejection is weak, across all rounds. My AR definitely pushed them out further. Gas isn't pushing back enough, is my guess, like others say.
 
So it locks back on an empty magazine? Not short stroking so not a gas issue.
Check your extractor and extractor spring and also check the ejector spring. If you remove the BCG and hook the rim of a case under the extractor and roll it in to compress the ejector then let it go it should flick the empty brass towards the extractor side. If it doesn't you need to replace the ejector spring or clean the ejector plunger hole so it moves freely.
If it passes that test inspect the extractor, it should have a good edge to it where it grabs the brass and not be rounded off or chipped.
 
This is a weird one, for sure. If it's locking back and has never failed to strip a round it shouldn't be a gas issue; since you've tried a dozen mags it shouldn't be a mag issue; and as you have swapped bolts with no improvement it doesn't seem to be an ejector or extractor problem.

That leaves ammo. But if you are ordering parts anyway I would get a new extractor and ejector, or at least springs for them. As much as you have theoretically ruled those out my experience is stovepipes are almost always related to those items.
 
Did it start as soon as you cracked a fresh crate of ammo?
How was ejection before you started having issues? Strong and to 4:00ish? Or was it erratic and/or weak but still worked?

If replacing the BCG did not fix it and you're sure your gas block is aligned, the gas tube isn't cracked or obstructed then it must either be an ammo issue or it's gummed up somewhere.
Did you change anything recently? Buffer? Have you cleaned the buffer tube out and made sure the buffer can stroke through unrestricted? Wish you lived closer, so much easier to diagnose with the rifle in my hands.
 
Come to think if it, there were some instances where it would eject and then jam with round number 9 caught partially up the feedramp with the bolt half closed on it. I figured it was a magazine thing as it didn't happen with all of the magazines. Could be an ammo thing as this is a new spam can but this is the fourth or fifth crate of the same ammo, although it's still Chinese surplus.

Pretty sure it has a new extractor, too, but could be mixing it up with a different rifle.

Might just be time for a new gas tube, extractor, springs and ejector. Maybe I'll throw in a new buffer spring too. "hello, Brownells? It's me again...." :)
 
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