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Thread: 11.5” Colt FBI Barrel Ejection

  1. #1
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    11.5” Colt FBI Barrel Ejection

    Built my first pistol upper. I bought a 11.5” Colt Heavy Commando barrel from Arms Unlimited. Came with shaved and pinned FSP gas block from Colt. AU claims this is an FBI HRT overrun.

    Went with this barrel because of its reported .069 gas port and accuracy. Also the price was great. Swapped out my unfired 16” barrel from a new 6920 I bought a few years ago...so upper, barrel, and BCG are all Colt.

    I wanted a properly gassed rifle for 50/50 suppressor use when I get that. Using a H2 buffer from SOLGW and the Colt buffer spring.

    Fired Federal XM 193 and the rounds are ejecting at 2 o’clock about 3-4 feet away with a slight but noticeable ding on the cases from the brass deflector. Fiocchi .223 ejects at 4 o’clock as does Brown Bear .223. No dings.

    With an H2 buffer and a .069 gas port I didn’t expect the ejection pattern from the full power ammo. I didn’t have a way to measure the GP when I had the GB off to put the rail on.

    Is this normal? Seems like it’s cycling pretty fast with FP ammo for a .069 GP. I understand ejection patterns have a lot of variables. Recoils feels similar to my 16” 6920.

    ——————————-
    Side note- swapped an Aimpoint pro off my other rifle and the first shot from the 11.5 upper was in the X at 50 yards! No need to rezero. Never thought that would happen! Barrel is about 1.5 MOA with a red dot and Geissele trigger
    "A flute without holes, is not a flute. A donut without a hole, is a Danish." - Ty Webb

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    Short Version- Replace the extractor spring with either a Colt M4 extractor spring or a Sprinco extractor spring.

    Why The Extractor Spring Needs To Be Replaced- The spring isn't placing enough tension on the extractor to hold the rim of cartridge to hold the cartridge against the bolt face through the entire cycle. The extractor is letting go of the case early and the ejector isn't able to fling the case out of the ejection port with enough speed. The case gets bounced forward and the mouth is catching on the leading edge of the ejection port causing the mouth to get dinged. The extractor spring will get weaker with use and the AR will start exhibiting a bolt over base malfunction and get worse from there.

    Replace your extractor spring with either a Colt M4 extractor spring or a Sprinco extractor spring with the black polymer insert. DO NOT USE AN O RING. Nearly all other extractor springs are marginal. Some makers will use an O ring, but that only covers up the fact they are using a marginal extractor spring to begin with. A friend and I did some troubleshooting on a newly built rifle made with quality parts with one exception- the extractor spring. The BCG group supplier used a marginal spring and an O ring and the AR exhibited a more advanced stage of the bolt over (cases were bouncing off the leading edge of the ejection port and bouncing back into the action) from the very start. This was confirmed by examining slow motion video of the malfunction as it occurred. Replacing the extractor spring fixed the problem.

    It's important is that AR owners learn to recognize the signs of marginal and failing extractor springs and how to properly solve the issue. Mouth dings are an early sign, followed by bolt overs & stovepipes, then bolt overs with an empty case caught in the action. If an extractor spring needs an O ring, the extractor spring is failing and needs to be replaced. If an O ring is used with the proper spring, too much tension will be placed on the extractor.

    Personal experience with my personal ARs and ARs of relatives and friends show that using Colt extractor springs ends bolt overs and empties caught in the action. I have never used Sprinco springs, but I.G. has plenty of experience with them and gives them his stamp of approval. Sionics uses Sprinco extractor springs in their ARs. Most other extractor springs are marginal at best and should be replaced.
    INSIDE PLAN OF BOX
    1. ROAD-RUNNER LIFTS GLASS OF WATER- PULLING UP MATCH
    2. MATCH SCRATCHES ON MATCH-BOX
    3. MATCH LIGHTS FUSE TO TNT
    4. BOOM!
    5. HA-HA!!

    -WILE E. COYOTE, AUTHOR OF "EVERYTHING I NEEDED TO KNOW IN LIFE, I LEARNED FROM GOLDBERG & MURPHY"

    http://i115.photobucket.com/albums/n289/SgtSongDog/AR%20Carbine/DSC_0114.jpg
    I am American

  3. #3
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    Quote Originally Posted by MistWolf View Post
    Short Version- Replace the extractor spring with either a Colt M4 extractor spring or a Sprinco extractor spring.

    Why The Extractor Spring Needs To Be Replaced- The spring isn't placing enough tension on the extractor to hold the rim of cartridge to hold the cartridge against the bolt face through the entire cycle. The extractor is letting go of the case early and the ejector isn't able to fling the case out of the ejection port with enough speed. The case gets bounced forward and the mouth is catching on the leading edge of the ejection port causing the mouth to get dinged. The extractor spring will get weaker with use and the AR will start exhibiting a bolt over base malfunction and get worse from there.

    Replace your extractor spring with either a Colt M4 extractor spring or a Sprinco extractor spring with the black polymer insert. DO NOT USE AN O RING. Nearly all other extractor springs are marginal. Some makers will use an O ring, but that only covers up the fact they are using a marginal extractor spring to begin with. A friend and I did some troubleshooting on a newly built rifle made with quality parts with one exception- the extractor spring. The BCG group supplier used a marginal spring and an O ring and the AR exhibited a more advanced stage of the bolt over (cases were bouncing off the leading edge of the ejection port and bouncing back into the action) from the very start. This was confirmed by examining slow motion video of the malfunction as it occurred. Replacing the extractor spring fixed the problem.

    It's important is that AR owners learn to recognize the signs of marginal and failing extractor springs and how to properly solve the issue. Mouth dings are an early sign, followed by bolt overs & stovepipes, then bolt overs with an empty case caught in the action. If an extractor spring needs an O ring, the extractor spring is failing and needs to be replaced. If an O ring is used with the proper spring, too much tension will be placed on the extractor.

    Personal experience with my personal ARs and ARs of relatives and friends show that using Colt extractor springs ends bolt overs and empties caught in the action. I have never used Sprinco springs, but I.G. has plenty of experience with them and gives them his stamp of approval. Sionics uses Sprinco extractor springs in their ARs. Most other extractor springs are marginal at best and should be replaced.
    I appreciate the advice but the BCG is a brand new Colt. BCG, Barrel, buffer spring, and Upper receiver were all brand new never fired Colt parts
    Last edited by OldState; 06-02-19 at 19:26.
    "A flute without holes, is not a flute. A donut without a hole, is a Danish." - Ty Webb

  4. #4
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    Quote Originally Posted by OldState View Post
    I appreciate the advice but the BCG is a brand new Colt. BCG, Barrel, buffer spring, and Upper receiver were all brand new never fired Colt parts
    Excellent choice of parts. While I'm a fan of the Colt springs and they've never given me a lick of trouble, I won't pretend they are infallible. The malfunction your AR is having is due to weak extraction and/or ejection. Colt coats everything with a preservative that can gum up the springs. I've had four Colts- two ARs and two 1911s- that wouldn't work right until I cleaned out all the preservative. It's possible your extractor/ejector is sticky from the goo. It's also possible it's got a bad spring.
    INSIDE PLAN OF BOX
    1. ROAD-RUNNER LIFTS GLASS OF WATER- PULLING UP MATCH
    2. MATCH SCRATCHES ON MATCH-BOX
    3. MATCH LIGHTS FUSE TO TNT
    4. BOOM!
    5. HA-HA!!

    -WILE E. COYOTE, AUTHOR OF "EVERYTHING I NEEDED TO KNOW IN LIFE, I LEARNED FROM GOLDBERG & MURPHY"

    http://i115.photobucket.com/albums/n289/SgtSongDog/AR%20Carbine/DSC_0114.jpg
    I am American

  5. #5
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    6857D187-FD45-4231-A0F2-0F9ADD40E00B.jpg3BA5E20B-D413-4A0B-97D8-38C282EF7A6E.jpgOk. I can take apart the BCG and clean it and see what that does. My gut feeling was that the gas port is larger than what I was lead to believe since ejection moved back as I shot weaker loads.

    This project began as a Colt 6920 OEM 1 so that is where the parts came from. The gun was new and in my safe for three years...so maybe the oil gummed up.

    I swapped the 16” barrel for the 11.5” Colt...which is supposed to be their FBI spec’d one. Then I put it on a LMT stripped “pistol” Lower I built up with a SOLGW LPK and a Geissele trigger and bolt catch.
    You may be able to see the mark on the Federal 193 brass. The cases from the other two loads had no such marks.
    "A flute without holes, is not a flute. A donut without a hole, is a Danish." - Ty Webb

  6. #6
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    The 069 port is a good size for non-suppressed use only.

    For mixed suppressed use, you're going to want smaller.

    Our EZTune gas tube is what you're looking for.
    Black River Tactical
    BRT OPTIMUM Barrels - 16" MPR, 14.5" MPC, 11.5" CQB, 9" PDW
    BRT OPTIMUM-S Barrel - 11.5" CQB Suppressor Gas Drive
    BRT OPTIMUM-S Barrel - 11.5" SB Suppressor, 11.5" SBT 25 Deg Tapered Shoulder Suppressor
    BRT Covert Comps 7.62, 5.56, 6X, 9mm
    BRT MarkBlue Gas Tubes - BRT EXT, EXC and PDW Lengths
    BRT EZTUNE Gas Tubes - CAR and MID
    BRT MicroPin Gas Blocks - .750" & .625"
    BRT MicroTUNE Adjustable Gas Blocks
    BRT CustomTUNE Gas Ports

  7. #7
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    Quote Originally Posted by Clint View Post
    The 069 port is a good size for non-suppressed use only.

    For mixed suppressed use, you're going to want smaller.

    Our EZTune gas tube is what you're looking for.
    I was just looking at those. But do you think a .069 port would through xm193 brass forward at 1-2 o’clock...with an H2 buffer? I hope it’s actually .069 and not bigger. What size tube/port size would you recommend then? I though .069 was small and specd that way because the intent was to use it mixed
    "A flute without holes, is not a flute. A donut without a hole, is a Danish." - Ty Webb

  8. #8
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    I need to work on my reading comprehension. I thought you were getting dents on the mouth of the case. In light of this, I'm almost certain I was wrong about the extractor spring. Still, I recommend cleaning out the gunk from the extractor and ejector.

    There are too many variables involved for the ejection pie chart to tell you anything about how an AR is gassed. But it can give an idea if something is up with the extractor and ejector.

    A .069" gas port isn't over gassed for unsuppressed use and an H2 buffer is always a good choice when the gas is right.
    INSIDE PLAN OF BOX
    1. ROAD-RUNNER LIFTS GLASS OF WATER- PULLING UP MATCH
    2. MATCH SCRATCHES ON MATCH-BOX
    3. MATCH LIGHTS FUSE TO TNT
    4. BOOM!
    5. HA-HA!!

    -WILE E. COYOTE, AUTHOR OF "EVERYTHING I NEEDED TO KNOW IN LIFE, I LEARNED FROM GOLDBERG & MURPHY"

    http://i115.photobucket.com/albums/n289/SgtSongDog/AR%20Carbine/DSC_0114.jpg
    I am American

  9. #9
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    My Sionics 11.5” Extreme Reduced Gas Port upper, which is made to be used with a suppressor (I have a direct thread Gemtech Trek -T attached to it), ejects brass about 2:30-3:00. Although it chucks the brass about 5-6 ft. I honestly haven’t paid attention to the brass. It shoots great and has been reliable.


    Sent from my iPhone using Tapatalk

  10. #10
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    With suppressor attached, correct? Is that suppressor known for high back pressure? What ammo and buffer? I think their ERGP has a GP size in the mid to low .06x’s

    The Sionics RGP was what I almost went with before I came across the deal on the Colt. Both are reported to have the same gas port...or very close. I preferred the profile of the Sionics but got the Colt for $250.

    I’m half tempted to buy pin gauges and measure the port size before I do anything else. All my research on these barrels said .069 port size and a representative of Arms Unlimited on TOS claims, emphatically, that these are FBI HRT barrels exclusive from Colt with the shaved FSP. However when I called their CS to confirm they were completely useless so I was trusting their rep on TOS.

    Maybe xm193 is hotter than I thought, but my 16” 6920 with an H buffer ejects that brass at 3:30 if I remember correct.
    "A flute without holes, is not a flute. A donut without a hole, is a Danish." - Ty Webb

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