View Full Version : 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.
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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
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.
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
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.
5753857539Ok. 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.
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.
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
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.
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
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.
~2:00 ejection with that setup is not too surprising.
Tube and port sizes are not exactly the same as barrel ports, so filling out the application info on the order page is best.
An 065 equivalent should work nicely for mixed use.
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
Thanks. Does that application mean someone will suggest a size? I filled it out but didn’t see where there would be communication.
The application info input is part of the ordering process.
If you select "BRT recommended size", we make the sizing determination during order fulfillment for your customized requirements.
Alternatively, you can send those same parameters to us at info@brt (spelled out) to get an answer back via email.
Thanks. Does that application mean someone will suggest a size? I filled it out but didn’t see where there would be communication.
For what it's worth, my Colt heavy 11.5" measured .069". A 1.75mm drill bit (.0689") fit very snug. Shouldn't matter, but mine doesn't have a FSB.
I put in a .0625 homemade port and run it with a M4SDII, A5H2 buffer, and Tubbs flat rifle (AR-10) spring.
For what it's worth, my Colt heavy 11.5" measured .069". A 1.75mm drill bit (.0689") fit very snug. Shouldn't matter, but mine doesn't have a FSB.
I put in a .0625 homemade port and run it with a M4SDII, A5H2 buffer, and Tubbs flat rifle (AR-10) spring.
I didn’t even think to test it with a drill bit. Now I’m not sure I feel like stripping it down to test. Curiosity may get me though....plus I’m not sure I want to try a “remedy” without determining the actual GP size.
Correct gas port size is key to optimal functioning in an AR, in my opinion. You would need to disassemble to install a port anyway. Personally, I like to know exactly what I have...
I have a bunch of drill bits in metric, #, inch, and letter sizes that cover .050-.095" in small increments. I decided to use bits instead of pin gauges because I make my own inserts and use the bits for both measuring and drilling.
With the tube or port solutions, the exact current size doesn't matter much.
The smaller secondary port takes over and drops the flow down to what you want.
With the tube or port solutions, the exact current size doesn't matter much.
The smaller secondary port takes over and drops the flow down to what you want.
I understand, but if the port is .069 already adding a .069 secondary port would be pointless for example. I think I need a point of reference to understand why this thing is ejecting the way it is. If I measure and find that it’s actually.076 that would play a part in my decision.
I think your tubes will be the best solution in the end.
everready73
06-05-19, 20:24
I understand, but if the port is .069 already adding a .069 secondary port would be pointless for example. I think I need a point of reference to understand why this thing is ejecting the way it is. If I measure and find that it’s actually.076 that would play a part in my decision.
I think your tubes will be the best solution in the end.
Appreciate an update if you do measure the port. I was going to order on of the barrels from AU, but having reservations
Anyone looking for a dedicated suppressed or 50/50 barrel should check out our 11.5" OPTIMUM CQB-S (https://www.blackrivertactical.com/concrete5/store/#!/BRT-11-5-OPTIMUM-CQB-S-Barrel-Suppressor-Gas-Drive/p/110419568/category=1852006)
Searching for something to measure but I will post it.
The barrel is a legit heavy FBI profile colt sealed in a blue bag. I’m just hoping that it was ported the same as others in the market.
Got sidetracked with a few weeks of travel for work on top of packet weekends. Also got discouraged looking for pin gauges to measure. I’m leaning heavily toward just getting one of your gas tubes but I would like to know the actual size of the GP.
556BlackRifle
06-22-19, 10:45
In addition to the excellent gas port advice above, check out the Vltor A5 H2 with Springco Green. I find it to be a very forgiving combo.
From personal experience AU is shady at best. The HRT barrels are not exclusive to AU.
Well to be specific they said the HRT barrel with the shaved FSP were exclusive to them. I have know idea if it’s true or not.
Sent a couple old drill bits your way to get this figured out.
Searching for something to measure but I will post it.
The barrel is a legit heavy FBI profile colt sealed in a blue bag. I’m just hoping that it was ported the same as others in the market.
Just received an email from a customer with three of these FBI barrels from AU.
He measured the ports with pin gauges at 073.
This would explain the hot cycling.
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.
Sent a couple old drill bits your way to get this figured out.
Thanks so much!
Just received an email from a customer with three of these FBI barrels from AU.
He measured the ports with pin gauges at 073.
This would explain the hot cycling.
Interesting. So if that turns out to be the case with mine, what size gas port/tube would you recommend? Would like it to still be able cycle Brown Bear, etc.
If the Crane spec for 10.5”s is .070 shouldn’t 11.5” be a bit smaller? Thanks!
.069 is a good size unsuppressed.
50/50 mixed can be smaller.
.069 is a good size unsuppressed.
50/50 mixed can be smaller.
Just got the bits. Hopefully I can get some time over the holiday weekend to put this apart and measure. I’ll report as soon as I know. Thanks again!!!
Just received an email from a customer with three of these FBI barrels from AU.
He measured the ports with pin gauges at 073.
This would explain the hot cycling.
5789957900
Well the mystery is solved. The bit you sent labeled .073 easily fit in. I measured the bit at .072 so I’m comfortable saying this is a .073 GP...not .069. Barrel is dated 9/17 if anyone is interested....not sure if you can see that in the second pic.
I’ll go ahead and order a tube from you. With the goal of 50/50 suppressed and wanting to be able run xm193 down to Brown Bear what would you recommend size wise? I’m heavily considering the new OSS 7.62 can or low back pressure design like the Dead Air Nomad.
Thanks again!
Once a Rifle, Always a Rifle
The BATFE has made it very clear that once a receiver is built into a rifle, whether by a factory or by you, it is always a rifle and converting it to a pistol is illegal.
OP are you using the upper on the same Colt lower?
Once a Rifle, Always a Rifle
The BATFE has made it very clear that once a receiver is built into a rifle, whether by a factory or by you, it is always a rifle and converting it to a pistol is illegal.
A pistol may be configured as a rifle, then reconfigured back into a pistol.
OP are you using the upper on the same Colt lower?
Reread post #5, 3rd paragraph.
Once a Rifle, Always a Rifle
The BATFE has made it very clear that once a receiver is built into a rifle, whether by a factory or by you, it is always a rifle and converting it to a pistol is illegal.
OP are you using the upper on the same Colt lower?
I appreciate your concern but as @mistwolf pointed out, I put this on an LMT lower that I bought stripped and built with a LPK.
There is an interesting wrinkle with this rifle though. I had sent the lower back to Colt because it had all types of file and tool marks on it. Colt said it was indeed “out of spec” and sent a new one. I asked if it was a virgin lower or if it was from a rifle. The guy I spoke to said he personally pulled it off the assembly line and it was never assembled into a rifle. I guess I could technically use it but I’ve decided to SBR it as planned. I like the idea of having an SBR and pistol lower.
To the original post, I just received the .069 tube from BRT. I was going to install it this weekend but got distracted with our AC going down. Will have to wait until next week but I will be sure to report the results.
56cbr600rr
10-16-19, 22:15
How it turn out?
I appreciate your concern but as @mistwolf pointed out, I put this on an LMT lower that I bought stripped and built with a LPK.
There is an interesting wrinkle with this rifle though. I had sent the lower back to Colt because it had all types of file and tool marks on it. Colt said it was indeed “out of spec” and sent a new one. I asked if it was a virgin lower or if it was from a rifle. The guy I spoke to said he personally pulled it off the assembly line and it was never assembled into a rifle. I guess I could technically use it but I’ve decided to SBR it as planned. I like the idea of having an SBR and pistol lower.
To the original post, I just received the .069 tube from BRT. I was going to install it this weekend but got distracted with our AC going down. Will have to wait until next week but I will be sure to report the results.
Sparky5019
10-21-19, 17:40
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.
Keep fighting the good fight brother. Lol. I’ve put Sprinco extractor springs in some really crappy guns over the years. Solves all kinds of badness. Lol.
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.
Sprinco has a enhanced and a extra power, which one is recommended? with or without the insert?
Sprinco has a enhanced and a extra power, which one is recommended? with or without the insert?
I'd go with a Colt "gold" spring, or one of SAW's green springs.
MorphCross
10-23-19, 17:01
Easy button: https://www.gandrtactical.com/Colt-Extractor-Spring-Assembly_p_322.html
Has anyone done a back to back comparison between the colt gold spring and the two sprinco options?
I'd go with a Colt "gold" spring, or one of SAW's green springs.
What is a SAW green spring?
http://www.specializedarmament.com/ar-15-bolt-group/extractor-spring-assembly-sa/
I think it is a reference to this.
How it turn out?
Great. With the H2 buffer and Colt spring it ejects m193 at 3 o’clock and .223 at 4. Brown Bear will not cycle. I want to see if a H1 buffer would allow for cheap Russian ammo to be used if needed. May have gone .070 in hindsight.
Dropping down in buffer weight speeds up the cycle and allows proper operation with lower power ammo.
Great. With the H2 buffer and Colt spring it ejects m193 at 3 o’clock and .223 at 4. Brown Bear will not cycle. I want to see if a H1 buffer would allow for cheap Russian ammo to be used if needed. May have gone .070 in hindsight.
Sprinco has a enhanced and a extra power, which one is recommended? with or without the insert?
With insert
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