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.
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.
shaved FSP were exclusive to them. I have know idea if it’s true or not.
Clint
July 1, 2019, 9:32pm
27
Sent a couple old drill bits your way to get this figured out.
Clint
July 2, 2019, 2:15am
28
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.
OldState:
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.
Thanks so much!
Clint:
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!
Clint
July 2, 2019, 4:53am
30
.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!!!
Clint:
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.
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!
JPS
July 15, 2019, 3:08am
33
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?
JPS:
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.
JPS:
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.
MistWolf:
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.
prepare
October 23, 2019, 12:00pm
38
MistWolf:
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?
WS6
October 23, 2019, 2:57pm
39
I’d go with a Colt “gold” spring, or one of SAW’s green springs.
