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Posted: 4/26/2014 4:43:07 PM EDT
[Last Edit: 4/26/2014 4:45:52 PM EDT by urbankaos04]
I just got a hold of a Colt 6720 upper and was just thinking about how overgassed this system really is?  I bought this upper initially thinking that I was going to have the barrel cut down to 14.5", but decided against it.  Now that I'm keeping the upper 'as-is' I was just wondering about what I could do to mitigate the issue and if it's really a problem at all.  Sometimes I think we get so wrapped around the axle about details that really don't matter in the end, as most of us don't shoot these things to the point that our concerns will really manifest themselves.   At any rate, thanks for any feedback.
Link Posted: 4/26/2014 4:52:00 PM EDT
Mine belches flame from the ejection port. I'm guessing I'm a tad overgassed.
Link Posted: 4/26/2014 4:52:05 PM EDT
I've never had any problems with a carbine length gas system with a 16" barrel.

I hear recoil impulse is a bit more but I wouldn't know, I've never shot a mid-length before to compare.
Link Posted: 4/26/2014 4:55:42 PM EDT
[Last Edit: 4/26/2014 4:56:13 PM EDT by MikeE23666]
I've never thought a 16" barreled AR with carbine gas system was over gassed.
Link Posted: 4/26/2014 5:00:43 PM EDT
You are fine. shoot as normal don't go searching for a solution to a problem that doesn't exist
Link Posted: 4/26/2014 5:02:39 PM EDT
You refer to it as an "issue", is it? Or is it just the interwebs who say it is an issue? Lots of people have put thousands and thousands of rounds through 16" barrels with carbine gas systems and never had an "issue". Don't let people fool you. That gun will run great.
Link Posted: 4/26/2014 5:02:42 PM EDT
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Originally Posted By patriot_man:
I've never had any problems with a carbine length gas system with a 16" barrel.

I hear recoil impulse is a bit more but I wouldn't know, I've never shot a mid-length before to compare.
View Quote


This.

I guess I'm just insensitive as I don't find a big difference between gas systems.
Link Posted: 4/26/2014 5:45:10 PM EDT
Originally Posted By urbankaos04:
I just got a hold of a Colt 6720 upper and was just thinking about how overgassed this system really is?  I bought this upper initially thinking that I was going to have the barrel cut down to 14.5", but decided against it.  Now that I'm keeping the upper 'as-is' I was just wondering about what I could do to mitigate the issue and if it's really a problem at all.  Sometimes I think we get so wrapped around the axle about details that really don't matter in the end, as most of us don't shoot these things to the point that our concerns will really manifest themselves.   At any rate, thanks for any feedback.
View Quote


Start here to understand the term "over-gassed". Take special note of the second chart, showing pressures and dwell times for different barrel and gas system lengths.

Gas system pressure is important at the two ends of the continuum: when excessively low, a dry, dirty gun may fail to cycle; when excessively high, shell cases may not successfully eject, and wind up back in the upper to cause an FTE. In-between excessively high and excessively low, pretty much anything that allows the gun to run successfully with the ammunition of choice is okay. Most barrel makers try to err on the side of larger gas ports and higher pressures, so as to avoid the problem of under-lubed or dirty guns failing to cycle, and the customer dissatisfaction that creates.

Gas blocks and even gas keys that are adjustable for pressure are available in the market, so depending upon how obsessive you feel, it's possible to tune an AR to be a pussycat. Up to you, or you can just run it.
Link Posted: 4/26/2014 6:20:07 PM EDT
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Originally Posted By MikeE23666:
I've never thought a 16" barreled AR with carbine gas system was over gassed.
View Quote


agreed....it's really much ado about nothing!  My 16" M&P 15T runs all day long........
Link Posted: 4/26/2014 6:27:32 PM EDT
It will look cooler cut to 14.5
Link Posted: 4/26/2014 6:40:14 PM EDT
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Originally Posted By KILLERB6:


This.

I guess I'm just insensitive as I don't find a big difference between gas systems.
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Originally Posted By KILLERB6:
Originally Posted By patriot_man:
I've never had any problems with a carbine length gas system with a 16" barrel.

I hear recoil impulse is a bit more but I wouldn't know, I've never shot a mid-length before to compare.


This.

I guess I'm just insensitive as I don't find a big difference between gas systems.



Pretty much same here, and I've owned both.

IMHO, a 16" should not be "over gassed" at all.
One only needs to use the proper gas hole and all is good.
For that matter with the wrong size gas port you could over gas a 14.5 middy.
Link Posted: 4/26/2014 6:57:36 PM EDT
Use an H2 or H3 buffer and it will not be an issue further. Feel the difference!
Link Posted: 4/26/2014 7:02:30 PM EDT

Discussion ForumsJump to Quoted PostQuote History
Originally Posted By GSMullins:
Start here to understand the term "over-gassed". Take special note of the second chart, showing pressures and dwell times for different barrel and gas system lengths.



Gas system pressure is important at the two ends of the continuum: when excessively low, a dry, dirty gun may fail to cycle; when excessively high, shell cases may not successfully eject, and wind up back in the upper to cause an FTE. In-between excessively high and excessively low, pretty much anything that allows the gun to run successfully with the ammunition of choice is okay. Most barrel makers try to err on the side of larger gas ports and higher pressures, so as to avoid the problem of under-lubed or dirty guns failing to cycle, and the customer dissatisfaction that creates.



Gas blocks and even gas keys that are adjustable for pressure are available in the market, so depending upon how obsessive you feel, it's possible to tune an AR to be a pussycat. Up to you, or you can just run it.
View Quote View All Quotes
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Originally Posted By GSMullins:



Originally Posted By urbankaos04:

I just got a hold of a Colt 6720 upper and was just thinking about how overgassed this system really is?  I bought this upper initially thinking that I was going to have the barrel cut down to 14.5", but decided against it.  Now that I'm keeping the upper 'as-is' I was just wondering about what I could do to mitigate the issue and if it's really a problem at all.  Sometimes I think we get so wrapped around the axle about details that really don't matter in the end, as most of us don't shoot these things to the point that our concerns will really manifest themselves.   At any rate, thanks for any feedback.




Start here to understand the term "over-gassed". Take special note of the second chart, showing pressures and dwell times for different barrel and gas system lengths.



Gas system pressure is important at the two ends of the continuum: when excessively low, a dry, dirty gun may fail to cycle; when excessively high, shell cases may not successfully eject, and wind up back in the upper to cause an FTE. In-between excessively high and excessively low, pretty much anything that allows the gun to run successfully with the ammunition of choice is okay. Most barrel makers try to err on the side of larger gas ports and higher pressures, so as to avoid the problem of under-lubed or dirty guns failing to cycle, and the customer dissatisfaction that creates.



Gas blocks and even gas keys that are adjustable for pressure are available in the market, so depending upon how obsessive you feel, it's possible to tune an AR to be a pussycat. Up to you, or you can just run it.
They focus too much on dwell time and leave out gas port size.  Still a good read, but the size of your gas port makes a big difference.

 
Link Posted: 4/26/2014 7:36:23 PM EDT
I hear you gas about the gas port size, but I don't think Colt uses a different gas ports size on their 16" barrels vs their 14.5" barrels.  At any rate, I was just curious what ARFCOM's thoughts would be.
Link Posted: 4/26/2014 8:12:22 PM EDT
The gas port should be .063, from what I've read colt is pretty good at keeping that spec.
My 16 carbine Windham is at .063 also and works well with a H2 buffer but had no issues with the carbine buffer it came with.

I plan on getting a adjustable gas block for it to experiment with at some time in the near future.
Link Posted: 4/26/2014 9:10:29 PM EDT
just try the spikes t2 buffer and see how it does.  worst case, it will short stroke, then you know its not over gassed.  best case, it will cycle a little less violently and recoil less.
Link Posted: 4/26/2014 9:10:37 PM EDT
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Originally Posted By urbankaos04:
I hear you gas about the gas port size, but I don't think Colt uses a different gas ports size on their 16" barrels vs their 14.5" barrels.  At any rate, I was just curious what ARFCOM's thoughts would be.
View Quote

The carrier moves 0.035 of an inch before the bolt unlocks. Which at this point all the pressure against the bolt's piston, the carrier uses to push off, is vented out the side of the carrier. Within a little more than a 32nd of an inch the bolt carrier group needs enough gas pressure to compress the action spring to where the buffer's urethane bumper touches the end of the lower receiver extension. A barrel's gas port is too large if it causes the urethane bumper to compress to the point the carrier/ gas key impacts the rear of the lower receiver.

From my understanding Colt uses the USGI M4 spec'd gas port for their 16" barrels as well which is 0.0625"/ 0.063". And, lastly below is an article by Mike Pannone, and also a report from the Aberdeen Proving Ground that are both good reads.

The Big M4 Myth by Mike Pannone

Comparison of a Theoretical and Experimental Study of the Gas System in the M16A1 Rifle
Link Posted: 4/26/2014 9:43:52 PM EDT
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Originally Posted By Bangz:
Use an H2 or H3 buffer and it will not be an issue further. Feel the difference!
View Quote

Link Posted: 4/27/2014 1:01:45 AM EDT
LMT Enhanced carrier, or VLTOR A5 should help. It's overgassed, but not by too much. I've heard that bolts will break more frequently.
Link Posted: 4/27/2014 3:16:03 AM EDT
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Originally Posted By Steelhead43:
The gas port should be .063, from what I've read colt is pretty good at keeping that spec.
My 16 carbine Windham is at .063 also and works well with a H2 buffer but had no issues with the carbine buffer it came with.

I plan on getting a adjustable gas block for it to experiment with at some time in the near future.
View Quote


Best I've used was carbine/14.5/.058". .063 is larger than I care for in 14.5 let alone 16".  But it works. Use an H2 buffer. H3 towards end of life.
Link Posted: 4/27/2014 3:27:18 AM EDT
If it runs fine it's not over gassed IMO.   I have all three gas systems and I really don't feel much recoil difference from carbin to midlength. My rifle length feels like there is less but it weighs almost two pounds more than my other guns so I assume that's why...


Just shoot it.
Link Posted: 4/27/2014 8:17:49 AM EDT
[Last Edit: 4/27/2014 8:47:49 AM EDT by urbankaos04]
The most I would do would be to use a heavier buffer, if even that.  I don't want to start messing around with different springs and buffers, but it seems that that is exactly what Pannone did, which worked out for him.  I'll see how it goes on Wednesday.  And, if anything, depending on how she shoots, I just may cut the barrel down to have the correct combo.  Ahhh, first world problems.  
Link Posted: 4/27/2014 8:19:46 AM EDT
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Originally Posted By Bangz:
Use an H2 or H3 buffer and it will not be an issue further. Feel the difference!
View Quote

if you want to be picky (which is what OP is thinking), if using H2 or H3 it still shoots fine, that means it's a bit overgassed with standard buffer, think about it
Link Posted: 4/27/2014 10:02:59 AM EDT
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Originally Posted By ragincajun1919:
You are fine. shoot as normal don't go searching for a solution to a problem that doesn't exist
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well said
Link Posted: 4/27/2014 10:23:52 AM EDT
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Originally Posted By Combat_Jack:


Best I've used was carbine/14.5/.058". .063 is larger than I care for in 14.5 let alone 16".  But it works. Use an H2 buffer. H3 towards end of life.
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Originally Posted By Combat_Jack:
Originally Posted By Steelhead43:
The gas port should be .063, from what I've read colt is pretty good at keeping that spec.
My 16 carbine Windham is at .063 also and works well with a H2 buffer but had no issues with the carbine buffer it came with.

I plan on getting a adjustable gas block for it to experiment with at some time in the near future.


Best I've used was carbine/14.5/.058". .063 is larger than I care for in 14.5 let alone 16".  But it works. Use an H2 buffer. H3 towards end of life.


A 16/carbine gas barrel would probably work great with that port also.
I notice a difference in BCG speed between my carbine and rifle gassed uppers.
I have no doubt that even a carbine gas barrel in spec are plenty generous with the gas flow.
I'm curious now small the port could be and still cycle PMC bronze or starting data reloads.
Link Posted: 4/27/2014 10:29:56 AM EDT
No idea, couldn't force myself to own anything longer than 14.5" with carbine gas tube...a 13.7 with KX3 and mid length tube shoots smooth as Astroglide.
Link Posted: 4/27/2014 10:45:30 AM EDT
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Originally Posted By nf9648:
No idea, couldn't force myself to own anything longer than 14.5" with carbine gas tube...a 13.7 with KX3 and mid length tube shoots smooth as Astroglide.
View Quote


That's kinda where I might be going... .   However, I'll see how it goes this Wednesday, first.   I'll be shooting XM193 to get a zero at 50 yds.  I'll then shoot some BH 69 grainers using a Leupold VXIII (4.5-14x) to see what it'll do with that at 100 yds.
Link Posted: 4/27/2014 1:48:49 PM EDT
Improving something doesn't necessarily mean that it's predecessor was a flawed design. That seems to be the opinion that is growing as time goes on. I own both gas systems. They have both been outstanding and I can hardly tell a difference.
Link Posted: 4/27/2014 8:42:05 PM EDT
They can all be tuned to run smooth.

The A5 or rifle buffer system is the biggest thing I've found for smoothing any AR out.

Many use adjustable gas blocks as well.

My carbine gas gun is a 10.5" and it's smooth as butter.

Link Posted: 4/28/2014 7:47:31 AM EDT
[Last Edit: 4/28/2014 7:54:07 AM EDT by RRAMODERATOR]
Link Posted: 4/28/2014 8:02:36 AM EDT
[Last Edit: 4/28/2014 8:05:33 AM EDT by urbankaos04]
Yeah, I hear ya, which is why I am not about to start using a bunch of different springs and buffers as I don't think there's that much of a real need to tune the upper to that extent. In the end, the worst thing that is going to happen is accelerated wear on some parts and mayyyyyybe a broken bolt if I was a high volume shooter, which I am not.
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