It sounds like a chamber issue to me. Of course this is simply internet diagnosing.
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Possible short chamber neck and or freebore or throat issue?
Don't sell yourself short, IG, you are right.
The DD barrel has a bad chamber. I located a shop near to me that had some go/no-go gauges and it didn't pass.
So, looks like I'll be contacting DD and see if they'll re-barrel this upper.
I thank you gentlemen for your time and expertise. Without the wealth of knowledge on this forum, many of us M4 owners
would be ships without a sail.
I hope this malfunction and diagnosis adds to the edification of this fine forum.
Just got the upper back from DD and they were unable to duplicate the FTE I was having and also said the chamber is within spec...which I'm a bit baffled as it didn't pass with a no-go gauge.
Here's what the troubleshoot team said:
"This afternoon we installed a bolt carrier group and a charging handle and attempted to replicate the customers condition by perform function testing in the 20 yard range using Federal XM193F, 5.56 M193 55gr ball ammunition.
The testing we performed was as followed:
1 – 30 round magazine on full auto
2 – Single shot rounds
1 – 30 round magazine on full auto
1 – 28 round magazine on full auto
1 – 20 round magazine on full auto
At this time the URG was allowed to cool after which the chamber was cleaned and polished. The brass was examined and the exterior condition of the casings showed signs of marring.
After cleaning and polishing 1 more 30 round magazine on full auto was cycled followed by 20 rounds at rapid fire. This brass was then examined and the condition of the casings was significantly improved.
We were not able to replicate the customers complaint and can find nothing functionally wrong with his barrel.
I don't know if signs of marring indicate that the chamber was likely the issue, but we will see when I put more rounds through it to test for myself (Aguila).
I am unconvinced that it had anything to do with the Aguila 55 grain ammo I was using, as I've shot 3K of that stuff through an identical upper without issue; It runs hot and clean. Further, I've run Wolf steel and gold through the identical upper, again, without issue.
If this upper doesn't run with the Aguila, it leaves little confidence that it will run with other types of .223 that I've used without issue for years.
Interesting read but after all is said and done if it still doesn't run why don't you put a Colt barrel on it and
start over? Pete
I hear what your saying Pete and I'm a big COLT fan. Between my Colt 6720s (2), my LMT M4 and the two builds mentioned with COLT, BCM and DD parts (barrel), I don't see that simply choosing a COLT barrel will be a better gamble.
On my first 6720, new, it came from the COLT factory with a bent, disfigured dust cover. How did that get past COLT QC? COLT wanted me to send the whole dang gun in. Replaced it myself, gun works perfectly. Second 6720, no issues, great gun. LMT, again, no issues...great gun.
Every BCM part I've laid my hands on = super duper. In fact, when comparing BCGs, I see the BCMs equal to the COLT BCGs (comparing the four that I own).
I'm driving at that, from these top four manufactures, all parts should be up to snuff-mil spec. This is the first issue I've had (aside from the dust cover) with any one part from any of the four.
This DD barrel should work as well and deliver, at minimum, equal performance to a BCM, LMT or COLT barrel.
So far, DD has handled it perfectly and I'll see if their chamber polishing did the trick.
If the DD barrel exhibits issues further, I'll give DD another shot. If that's to no avail, I'll sell the upper with full disclosure and probably pick up a BCM LW upper for this build and drive on.
Just my limited experience...YMMV.
It's possible the cases were annealed incorrectly and the rims are too soft. It's happened before