11.5 BCM possible buffer issues

[Animal_Mother556]

I know......I know....another 11.5 buffer question.

The problem is, it seems like everyone has luck with different weights:
"My 11.5 BCM has run perfectly with H"
"BCM specifically designed the 11.5 to run with standard buffers"
"I run an H2 and it is fine"


Anyway...when building my first AR with less than 16 inch barrel I decided to just split the difference and use an H buffer.

Just had her at the range to zero it and out of approximately 50 rounds, I had about 6 of these. Magazines were a mix of older pmags, new generation 20 round mags, and D&H GI mags. Ammo was Independence 55gr 5.56.

I've never seen this particular malfunction with an AR, but my gut says it is a buffer issue. Could it be a break-in issue?

[Animal_Mother556]

What I should have done was load one round in a bunch of mags and check for bolt lock. But I am dumb and forgot....

[C4IGrant]

That ammo sucks. Switch that out first and then try again.

Did you install the GB or did BCM?


C4

[Animal_Mother556]

Alright, I have some other 5.56 I can try.

BCM installed FSB, but I chopped it off pretty much as soon as ai got it. Chopped it without removing it from the gun, which I have done numerous times.

[MistWolf]

Extraction problem. Extractor is losing control of the empty before it can be ejected

[Animal_Mother556]

So, a heavier buffer to slow the bolt down?

[MistWolf]

Replace the extractor spring. Inspect the extractor for damage and wear.

We know it's an extraction issue and not under or over gassing. If under gassed, the rifle would simply not lock back on the last round, or not cycle far enough for clean ejection without stripping the next round from the magazine.

If the rifle were simply over gassed, it would be flinging brass into the next area code. If the excessive carrier speed is causing the extractor to "jump the rim" it's because the spring is weakened but still strong enough to hold the rim during normal speeds. Changing to a heavier buffer may stop the problem, but since the spring is starting to fail, it's only a matter of time until it weakens enough that the problem will return.

Replace the spring and inspect the extractor. I suggest getting the copper colored Colt extractor spring with the black insert. Do not use any kind of o ring. The o ring will place too much tension one the extractor. Last time I checked, Midway had Colt extractor springs for about $5 a piece plus whatever they charge for shipping. Brownell's is a little cheaper, but are on backorder

[Iraqgunz]

All other guessing aside, Federal Independence is way too hot and I wouldn't put it anywhere near anything I own.

You are using too light of a buffer. A BCM 11.5" will run an H2 all day long, and an H3 with good lube and MILSPEC ammo.

[zk556x45]

An extractor spring up-grade and an H2 should resolve this. I've had good luck with the BCM extractor up-grade kits, but MistWolf advises against. YMMV.

[ST911]

Ammo was Independence 55gr 5.56.

There are known and documented issues with the Federal-Independence XM193i. Here is a thread with additional information, including velocities and lot numbers for reference. https://www.m4carbine.net/showthread.php?153680-Update-Independence-5-56-XM193I

[Animal_Mother556]

Thanks a bunch, guys.

For the record, the BCG was also brand new just like the upper....I shall get some colt springs and extractor inserts and perhaps a chunk of tungsten from Geissele to turn this buffer up one notch.

Also, I had no idea about the Independence ammo being poop. I have some black box Federal to try.

Thanks again, gents. Truly appreciated.

[Animal_Mother556]

Just googled the lot number of my ammo and came up with this from this forum....

"Lot# FC13F001-059
High pressure signs and dropped primers at a rate of about 10%. Guns included known-good BCM SBR (11.5") and a Colt 6520 (16") with unblemished performance records."

I have shot close to 1000 rounds of this stuff through numerous different 20 and 16 inch ARs....holy crap.

Every time I policed brass (which wasn't all the time, mind you) I never noticed any pressure signs. I am glad I know about this now.

[MistWolf]

An extractor spring up-grade and an H2 should resolve this. I've had good luck with the BCM extractor up-grade kits, but MistWolf advises against. YMMV.

This is where my poor note keeping bites me in the butt. In my research, I came across information about the extractor spring from good source. It explained that the original extractor spring worked fine in a 20 inch rifle, but didn't provide enough tension when used in the carbine. An o ring was used as a temporary fix until a permanent fix could be devised. Colt developed the copper, five coil spring with black insert which fixed the problem. But, if an o ring is used with this setup, extractor tension is too high and if I recall, interferes with ejection. Unfortunately, I don't recall where I found this information and haven't been able to find the source since which I find frustrating. I also admit that I'm lazy and find it easier to simply state "don't use an o ring" than to go into a detailed explanation why.

I have experienced the very same malfunction in two of my ARs with four different bolts. One bolt was from PSA, two were brand new cheapies of an unknown source given to me by a friend and one an LMT Enhanced bolt. In each case, the malfunction was traced to a weak spring. The PSA spring gave up the ghost after two or three thousand rounds and the unknowns after four or five hundred. The extractor springs in the LMT Enhanced bolt (it uses two) were too soft right from the start.

I've also followed several threads online, started by shooters asking for help with fixing this same malfunction. In each case, the problem was either a weak spring or a worn or damaged extractor. Usually it was the spring. I don't recall in any of these cases where the worn spring was a Colt spring. That doesn't mean I don't think the Colt spring will not wear out. All springs wear out eventually. But, I take it as anecdotal evidence Colt got it right.

I don't know everything and chances are, I really don't know enough. But I've made a career of troubleshooting and repairing aircraft and their systems and I've been applying that experience and skill set to ARs while trying to figure them out

[Iraqgunz]

Is this a new BCM BCG or used? If this is new I would suggest contacting BCM as the standard extractor spring should be fine. I also wouldn't dick around with the build a buffer nonsense. Just get an H2 and be done with it.

[Animal_Mother556]

New BCG, new upper.

I think my first order of business will be to feed it some known quality ammo and see what's what after checking on the extractor and springs to see if there are any odd things going on there.

[MistWolf]

I recently had issues with an extractor spring on a brand new Colt getting gunned up with preservative because I didn't clean it out from behind the extractor before shooting it. The preservative was gumming it up