9mm AR Double feed/FTE

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870Mike
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9mm AR Double feed/FTE

Post by 870Mike » Fri Jun 10, 2016 10:27 pm

My 9mm AR build is giving me grief. It was built with quality parts, but is a jam-o-matic.

Using 30rd. Colt magazines, it will fire for the first 3 rounds or so, then stop. Upon examination, I find a new round (almost) in the chamber, and the previous spent casing sitting sideways, either stove-piped or tangled in the front of the bolt.

I'm guessing one of two things:

1) The ejection of the fired round isn't strong enough to get that casing out of the way fast enough or...

2) The bolt is travelling too fast, preventing proper function.

How does one test the ejection?

Would a heavier buffer and/or spring slow down the bolt?

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Re: 9mm AR Double feed/FTE

Post by 305tillimoved » Fri Jun 10, 2016 10:34 pm

Might be excessive bolt travel. Do you have any sort of spacer in your buffer tube? Thats what fixed the exact same issue for me.
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Re: 9mm AR Double feed/FTE

Post by John K » Fri Jun 10, 2016 11:49 pm

Ammo? Barrel length? Whose bolt? Which buffer and spring?

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Re: 9mm AR Double feed/FTE

Post by 870Mike » Sat Jun 11, 2016 6:19 am

305tillimoved wrote:Might be excessive bolt travel. Do you have any sort of spacer in your buffer tube? Thats what fixed the exact same issue for me.
I added a stack of quarters in the buffer tube to act as a spacer. Perhaps I need more quarters? About $1.75 in there now.
Last edited by 870Mike on Sat Jun 11, 2016 6:31 am, edited 1 time in total.
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Re: 9mm AR Double feed/FTE

Post by 870Mike » Sat Jun 11, 2016 6:29 am

John K wrote:Ammo? Barrel length? Whose bolt? Which buffer and spring?
Ammo is new Federal 115gr. brass.
Barrel is 10"
CMMG ramped bolt.
Will have to look up the paperwork, but I researched the heck out of this as I built it. I'm certain the buffer/spring is what was recommended for a 9mm. I'll either look up the paperwork or weigh the bolt a little later and report back.
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Re: 9mm AR Double feed/FTE

Post by better2have&notneed » Sat Jun 11, 2016 10:57 am

305tillimoved wrote:Might be excessive bolt travel. Do you have any sort of spacer in your buffer tube? Thats what fixed the exact same issue for me.
Same for me. Mine jammed every other round until I put in quarters and a spikes tactical spacer....also using spikes 9mm buffer.
I added quarters until the bolt recoils just a hair past the bolt catch. Mine broke bolt catches after 200ish rounds....not anymore.
And those CMMG colt 9mm mags can go right in the garbage too.

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Re: 9mm AR Double feed/FTE

Post by 305tillimoved » Sat Jun 11, 2016 11:13 am

870Mike wrote:
305tillimoved wrote:Might be excessive bolt travel. Do you have any sort of spacer in your buffer tube? Thats what fixed the exact same issue for me.
I added a stack of quarters in the buffer tube to act as a spacer. Perhaps I need more quarters? About $1.75 in there now.
Question is, did you have the problem BEFORE adding the quarters?
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Re: 9mm AR Double feed/FTE

Post by 870Mike » Sat Jun 11, 2016 1:02 pm

305tillimoved wrote:Question is, did you have the problem BEFORE adding the quarters?
Never fired it without the spacer quarters. Those were installed on Day 1.
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Re: 9mm AR Double feed/FTE

Post by 870Mike » Sat Jun 11, 2016 1:04 pm

better2have&notneed wrote:And those CMMG colt 9mm mags can go right in the garbage too.
The mags aren't CMMG, just the bolt. Mags (Colt?) function perfectly in my 9mm SBR, so I know/think they're not the issue.
Last edited by 870Mike on Sat Jun 11, 2016 1:05 pm, edited 1 time in total.
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Re: 9mm AR Double feed/FTE

Post by 305tillimoved » Sat Jun 11, 2016 1:05 pm

870Mike wrote:
305tillimoved wrote:Question is, did you have the problem BEFORE adding the quarters?
Never fired it without the spacer quarters. Those were installed on Day 1.
Try removing the quarters first and see what happens. If youre using a dedicated 9mm bolt and spring you might not need the spacer.
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Re: 9mm AR Double feed/FTE

Post by 870Mike » Sat Jun 11, 2016 1:06 pm

That's worth a shot (no pun intended) and if it works, I'll have an extra $1.75 in my pocket.
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Re: 9mm AR Double feed/FTE

Post by 870Mike » Sat Jun 11, 2016 1:11 pm

I sniffed around on ArfCom and this seems to be a fairly common issue. Two of the resolutions involved tweaking the ejector. :-k
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Re: 9mm AR Double feed/FTE

Post by 870Mike » Sat Jun 11, 2016 1:16 pm

Looking at the paper-work now...

1 - RRA Dedicated 9mm Carbine Buffer.

I don't see a separate receipt for the spring, so I'm assuming spring was included...

1 - CMMG AR-9 Complete 9mm Bolt Assembly

The CMMG AR-9 Complete 9mm Bolt Assembly is intended to work with CMMG's Mk9 dedicated 9mm AR15 system, but can also work with many other 9mm uppers and AR15 builds. Made of 8620 tool steel, the bolt and carrier are incorporated into a single body due to the straight blowback design of 9mm AR15s. The "gas key" becomes a charging handle interface, the extractor is a proprietary design, and there is no ejector (the ejector is located on the lower receiver in 9mm builds).

This bolt is ramped correctly underneath to allow it to function properly with both notched 9mm spec and standard AR15 spec hammers. No special hammer needed!
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Re: 9mm AR Double feed/FTE

Post by better2have&notneed » Sat Jun 11, 2016 5:28 pm

870Mike wrote:
better2have&notneed wrote:And those CMMG colt 9mm mags can go right in the garbage too.
The mags aren't CMMG, just the bolt. Mags (Colt?) function perfectly in my 9mm SBR, so I know/think they're not the issue.
Sorry for the poor wording...shoulda said "CMMMG Colt 9mm mags SUCK, don't buy them".

Also, I just remembered that the bottom of my bolt carrier would built up a lot of "copper coating" from the bullet jackets. It was fairly smooth, but still a little ruff so I used a 700(?) grit knife sharpener to smooth it out...no more copper build-up. I did that right after I built mine, when I was having problems. I don't remember exactly what solved my problem though.

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Re: 9mm AR Double feed/FTE

Post by Racist Infidel » Wed Jun 29, 2016 12:00 am

Pull the BCG, put a live round under the extractor hooks. Hold the BCG by the butt end with the cartridge hanging off the extractor. With the breech end of the BCG hanging down, swirl the BCG in a conical motion, maybe a 3 or 4 inch circle at the end.

What happens?

[smilie=popcorn.gif]

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Re: 9mm AR Double feed/FTE

Post by cubanstang50 » Thu Jun 30, 2016 5:26 pm

Used to have the same problem plus light primer strikes. I have an ar10 buffer spring with a 9mm steel buffer. I shot it and all these problems came about. [smilie=014.gif] I was using freedom hush 165 grain. I changed the hammer spring to a 9mm hammer and took it to the range 2 week ago. I do not have the jams but i still get the light primer strikes, this time i just used perfecta 9mm 115 grain. So now i dropped $2 in quarters in the tube and am gonna take it back possibly tomorrow and see if it all fixed.

I was talking to a gun guru and he told me he uses the 12 ounce buffer for his 9mm and it works like a charm. The thing is the 12 ounce buffer is 140 bucks. I will get back and report.
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Re: 9mm AR Double feed/FTE

Post by Augdawg » Mon Jul 04, 2016 6:53 am

I also had the same problem (CMMG 9mm Rifle), I tweaked the ejector and didn't have the problem afterwards.

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Re: 9mm AR Double feed/FTE

Post by 870Mike » Tue Jul 05, 2016 5:46 pm

Augdawg wrote:I also had the same problem (CMMG 9mm Rifle), I tweaked the ejector and didn't have the problem afterwards.
Yeah, I read quite a bit about that. Tweaked it and hopefully test-firing tomorrow. Will report back with results for those similarly situated.
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Re: 9mm AR Double feed/FTE

Post by cubanstang50 » Mon Jul 11, 2016 9:28 pm

So i took the 9mm to the range and it failed again. So now i bought a wolff power spring and a 9mm-Q Buffer - 8.5 ounces. This should solve all my problems.
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Re: 9mm AR Double feed/FTE

Post by 870Mike » Tue Aug 09, 2016 8:14 pm

Update: Fixed it.

Seemed to be a combination of two evils...a misadjusted ejector and a C-Mags magazine.

Tweaked the ejector and tried a Spikes and a Metalform (Colt?) mag. Shot almost 100 rds. through it tonight, including rapid-fire. It ran flawlessly.

Ejector/bolt face gotsa look like this:

Image

The C-Mag with the blocky orange follower? Toss it.

Image
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