FTE on AR-15 upper chambered in 223/5.56

So last night after logging off, I started to take apart the upper and what do I find? A piece of broken shell casing in the area outside the chamber. This was from the first FTE that I experienced from a month or so ago. The casing was brass and part of the butt of the casing next to the primer broke off. That may not be 100% of why the extraction process didn't work as well as it should, but it may be part. I'm going to do some more investigation after work today checking gas block and port.... BPT I'll let you know what I find. If I'm still stumped, I'll definitely have to pay you a visit.

Thanks again for all the help!

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Originally Posted by BPTactical

Look in your other hand...........

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Ahh... There they are.

Thanks.

[Beer]

Quote:

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Originally Posted by ghettoblaster

So last night after logging off, I started to take apart the upper and what do I find? A piece of broken shell casing in the area outside the chamber. This was from the first FTE that I experienced from a month or so ago. The casing was brass and part of the butt of the casing next to the primer broke off. That may not be 100% of why the extraction process didn't work as well as it should, but it may be part. I'm going to do some more investigation after work today checking gas block and port.... BPT I'll let you know what I find. If I'm still stumped, I'll definitely have to pay you a visit.

Thanks again for all the help!

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This sheds a bit of light on the subject. There are a few things we need to check.
Headspace-excessive headspace can cause a casehead blowout and it can also bulge the case sufficiently enough to cause extraction issues.
Extractor condition, although if it is gripping sufficiently to pull the rim unlikely.
Chamber-if it has any annular machine marks or roughness they can grab a case to the point it won't extract.
Gas pressure-an over gassed gun can cause the issue you are having for a couple of reasons:
If the gas pressure is too high when the unlock/extraction cycle starts the case is still firmly expanded in the chamber and can stick the case.
Insufficient headspace can crowd the round into the rifling, causing a pressure spike similar to an overgassed situation and give the same result.

When the empty case was left in the chamber did it extract by hand easily or did you need to knock it out with a cleaning rod?

It is entirely possible that the chunk of casing was retarding the bolt unlocking and throwing the timing off which could cause the issue as well.

Wow, I used the word "retarding" in a totally legit and coherent manner..........

BPT - I had to use a cleaning rod to knock it out in both cases (brass casing and steel casing). When I found the chunk of casing, it was crammed to the rear of the chamber head space which may have been crowding the round into the rifling as you say. Would you say the best way to test this theory is to fire it again, one round at a time, or is there a better method for assuring that everything is set up properly?

I would try the single round method for a few shots-Single round from the mag and see if you:
1-get clean and consistent extraction.
2-bolt locks back as intended.

Use a standard GI metal mag, they always work. Some rifles have shown issues with Pmags and Tapco, well they are Tapco mags.

Save your brass and inspect it for any anomalies.

If all seems well step up your mag load to 3 rounds and see how she runs. If all is well let her run, if not come see me.

Hey BPT - just got back from the range. Here's my observations:

1) The round fires, the bolt locks back, but the casing does not eject. Had to use a cleaning rod to push it back out.
2) When I finally get the casing out, I can tell that the extractor ripped off/sheared the rim of the casing. So perhaps it's only stuck in there because it's getting yanked so hard it snaps the rim.
3) After that I switched lowers and put it on the other that I built which I had just used and I know works. In this case, it worked flawlessly: round fired, case ejected, bolt locked back, no problems at all.

So I'm starting to think maybe the buffer spring isn't strong enough on the buttstock. When I compare the pull on both rifles, the one with the problems seems a bit lighter to me. Lighter spring = faster action = sheared casing rims? That's my theory. What else could it be and how can I test it?

At least I know the upper works fine. Handled the round like a champ and plenty accurate. Bad news: may need new parts on the lower.

Suggestions?

One thing I don't think we ever established. Rifle or carbine?
Check for the correct spring.

From:
TECHNICAL MANUAL
ARMY NO. 9-1005-319-23&P
AIR FORCE TO 11W3-5-5-42

RIFLE: 11 3/4 Inches (29 85 cm)
minimum to 13 1./2 inches (34 29 cm)
maximum

CARBINE: 10 1/16 inches (25.56 cm)
minimum to 11 1/4 inches (28.58 cm)
maximum.

What weight buffer if a carbine, should be an H or H2.

Carbine, 16 inch barrel. I'm thinking maybe I ought to replace the entire butt stock (cause it's fun anyway!). But before I do, is there anything else I'm missing that might possibly be wrong?