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Posted: 7/26/2016 8:29:44 PM EDT
Here's a topic I haven't seen discussed in the last 5 years.
Just by looking at it, I can see the design intent was to trick a pistol/carbine-length gas system into thinking it was a mid-length (or perhaps a rifle length) one. Sounds plausible in theory since the "dwell" time is manipulated. So what's the flaw and if there isn't one, why isn't it more popular? Pics for reference:   |
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Posted: 7/26/2016 8:37:01 PM EDT
[#1]
Bump. I'd like to know, too
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Posted: 7/26/2016 8:43:44 PM EDT
[#2]
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Posted: 7/26/2016 8:47:42 PM EDT
[#3]
It doesn't change the physical location of the gas port on the barrel.
The entire tube is filled with air, no matter how long it is, as soon as you blow in one end air comes out the other end. it is not like you are dropping a single pellet in the tube and waiting for it to come out the other side, it is a column of air. |
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Posted: 7/26/2016 9:41:37 PM EDT
[#4]
Quote HistoryThanks for the link. It sounds like a couple people liked it. The only thing I could see it doing is minutely reducing the acceleration of the bolt pushing back into the breach in order to unlock. I totally get the gas in/gas out point and that the length of the tube has no pronounced effect. The thing that interests me is the relatively large increase in volume in the gas tube itself. It is harder to pump air into a road bike tire than a mountain bike one because you start compressing the air a lot sooner with the lower volume of the road bike tire. Keeping that in mind, the pistol tube is like the road bike tire. It doesn't take much gas before it is compressed enough to forcefully act on the bolt piston. With the pigtail, it would take longer to build the gas tube pressure to the same point. This is all happening in microseconds so I doubt the end user truly would feel a dampened recoil experience, but according to the laws of physics, it is happening. Interesting but I have no desire to purchase one. |
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Posted: 7/26/2016 9:54:55 PM EDT
[#5]
You could get the same effect by placing the gas port closer to the end of the barrel: less reliable.
Your getting the same impulse of gas but now it's in a longer tube so it'll exert less force on the bcg. It's a gimmick that reduces reliability |
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Posted: 7/26/2016 10:00:52 PM EDT
[#6]
Waste of time and money.
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Posted: 7/26/2016 10:06:24 PM EDT
[#7]
Quote HistoryQuoted: You could get the same effect by placing the gas port closer to the end of the barrel: less reliable. Your getting the same impulse of gas but now it's in a longer tube so it'll exert less force on the bcg. It's a gimmick that reduces reliability The industry actually moved the gas port further out on 16" barrels (hence the mid-length gas sytem). They did it in order to mimic the way the gas system operates on a 14.5" carbine-length barrel. It did not prove less reliable. It theoretically has reduced wear and tear on components. Also, it is not exactly the same impulse. It is a dampened impulse (minutely). That said, I agree that for all intents and purposes, it is gimmicky. |
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Posted: 7/29/2016 10:31:41 AM EDT
[#8]
Quote HistoryQuoted:
It doesn't change the physical location of the gas port on the barrel.The entire tube is filled with air, no matter how long it is, as soon as you blow in one end air comes out the other end. it is not like you are dropping a single pellet in the tube and waiting for it to come out the other side, it is a column of air. Atmospheric pressure is not applying directional force. It takes a high pressure impulse to unlock the bolt/push the bcg back. More volume in the gas tube will take more time to reach the same pressure, or will not reach the same pressure. Is another 2 inches in length enough to make a noticeable difference? No. If a company really wanted to make a gas tube that would slow down the unlock time and apply less force to the bcg then an expansion chamber in the gas tube that dramatically increases its internal volume would be effective. Adjustable gas block is still the right way to do it. |
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Posted: 7/29/2016 10:40:23 AM EDT
[#9]
Quoted:
. So what's the flaw and if there isn't one, why isn't it more popular? they tend to break along the curly part when used heavily. a fix to a problem when sbrs were not made correctly, ie early lmts/colts/etc eta there used to be a sticky in the c3/sbr forum about the 10" lmts and a couple post about it as a bandaid |
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Posted: 7/29/2016 11:35:56 AM EDT
[#10]
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Posted: 7/29/2016 1:05:31 PM EDT
[#11]
Quote HistoryQuoted:
Is another 2 inches in length enough to make a noticeable difference? No. Adjustable gas block is still the right way to do it. 1) you would be surprised. 2) adjustable gas blocks only change the gas pressure, not the dwell time, or the time unlocking starts. The correct solution is proper porting (or and adjustable block) and a proper weight buffer. The reason they lost popularity is stated above. |
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Posted: 7/29/2016 2:17:40 PM EDT
[#12]
Cue the "it doesn't work that way" gif.
Midlength or rifle length gas systems don't work the way they do because of the length of the gas tube, they work that way because of the location of the gas port on the barrel. These tubes are basically snake oil. |
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Posted: 7/29/2016 3:34:25 PM EDT
[#13]
With the pigtail tube, that I have, you can not use slim keymod or mlok handguards
 . Other than that I've had no other problems with them. I have had no problems with ordinary pistol length gas tubes either.
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Posted: 7/29/2016 4:16:23 PM EDT
[#14]
Quote HistoryQuoted:
Cue the "it doesn't work that way" gif. Midlength or rifle length gas systems don't work the way they do because of the length of the gas tube, they work that way because of the location of the gas port on the barrel. These tubes are basically snake oil. they are not snake oil, they do slow a gun down. The longer tube allows the pressure to fall since the bullet will be farther past the gas port by the time the gas hits the key. It basically fakes a gas port movement have you shot one??? |
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Posted: 7/29/2016 6:13:44 PM EDT
[#15]
Quote HistoryQuoted:
they are not snake oil, they do slow a gun down. The longer tube allows the pressure to fall since the bullet will be farther past the gas port by the time the gas hits the key. It basically fakes a gas port movement have you shot one??? Quote HistoryQuoted:
Quoted:
Cue the "it doesn't work that way" gif. Midlength or rifle length gas systems don't work the way they do because of the length of the gas tube, they work that way because of the location of the gas port on the barrel. These tubes are basically snake oil. they are not snake oil, they do slow a gun down. The longer tube allows the pressure to fall since the bullet will be farther past the gas port by the time the gas hits the key. It basically fakes a gas port movement have you shot one??? This seems logical. For a 16" with a carbine gas port, if longer pigtail tube delays gas reaching and activating the bolt, it should then have a recoil operation and impulse like a midlength. What am I missing? |
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Posted: 7/29/2016 7:30:57 PM EDT
[#16]
I'm more in line with Gamma on this one.
It's more the dwell time in regards to positioning of the gas port on the barrel than simply the length of the tube. |
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Posted: 7/29/2016 7:35:59 PM EDT
[#17]
Here is a simple thought exercise:
Gun A: has a gas tube with the ID the size of a McDonald's drinking straw. Gun B: Identical to Gun A except that it has a standard mil-spec gas tube. Would both guns behave the same or would the Gun A exhibit a delayed action upon the BCG? |
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Posted: 7/29/2016 7:38:55 PM EDT
[#18]
Quote HistoryQuoted:
Here is a simple thought exercise: Gun A: has a gas tube with the ID the size of a McDonald's drinking straw. Gun B: Identical to Gun A except that it has a standard mil-spec gas tube. Would both guns behave the same or would the Gun A exhibit a delayed action upon the BCG? Gas port hole size needs to be considered. |
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Posted: 7/29/2016 8:14:11 PM EDT
[#19]
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Posted: 7/29/2016 9:31:49 PM EDT
[#20]
Quote HistoryQuoted: Gas port hole size needs to be considered. Quote HistoryQuoted: Quoted: Here is a simple thought exercise: Gun A: has a gas tube with the ID the size of a McDonald's drinking straw. Gun B: Identical to Gun A except that it has a standard mil-spec gas tube. Would both guns behave the same or would the Gun A exhibit a delayed action upon the BCG? Gas port hole size needs to be considered. True... Let's say .076" on a carbine length 16" barrel. |
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Posted: 7/29/2016 9:34:09 PM EDT
[#21]
Quote HistoryQuoted: There is still one other option....the PRI Fatboy gas tube. It has a larger internal diameter. http://i135.photobucket.com/albums/q125/PursuitSS/Bolt%20Carriers/0D3562F8-B323-43A3-A424-C7524FB60EAF.jpg Good find! In essence, this is what the pig tail does. It increases the volume between the gas block and the gas key on the BCG.
Looks like the Fatboy is/was produced by a reputable company as well. |
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Posted: 7/29/2016 9:52:06 PM EDT
[#22]
I can't find it right now, but I recall a write up of a guy who bent his own gas tube on a custom AR-10 that was giving him trouble (rifle length)I think he ended up with about six loops- he was looking to increase the dwell until the chamber pressure had dropped enough to smooth extraction.
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Posted: 7/30/2016 1:09:30 AM EDT
[#23]
The pressure at the end of a short pressurized system will be higher than the pressure at the end of a longer pressurized system (with the same given pressure on the front end).
A pigtail system adds length and decreases pressure at the end. You could theoretically accomplish the same thing with a larger diameter tube, pressure decreases proportional to the 4th power of the radius. radius to the 4th power. Small increases in diameter result in large pressure changes. Think breathing through a hose or through a straw with a tube of the same length. Just a guess, but I'm thinking turbulence in the tube and heat burnout might be why they are not more popular in short gas systems. Also, yes, gas port does make a difference , but that is just a constriction in the tube, think of it as just part of the gas system. |
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Posted: 7/30/2016 1:19:25 AM EDT
[#24]
Quote HistoryQuoted:
Cue the "it doesn't work that way" gif. Midlength or rifle length gas systems don't work the way they do because of the length of the gas tube, they work that way because of the location of the gas port on the barrel. These tubes are basically snake oil. You might want to re think the way you phrased this. The location of the gas port on the barrel directly determines the length of the gas tube. Changing the length of the gas tube in any way does absolutely change the pressure curve. Poiseuille's law. Adding pigtails or changing tube diameter changes pressure at the business end. |
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Posted: 7/30/2016 1:58:21 AM EDT
[#25]
Quote HistoryQuoted:
IIRC, it was an attempt to TRY and achieve the same results that Tim LaFrance did with his patented "Twin Tube Gas System" that he designed for his M-16k By ALL reports, the M-16k was extremely reliable. <a href="http://s135.photobucket.com/user/PursuitSS/media/Bolt%20Carriers/23031DC5-5EB3-4B3F-8A14-D43C31451924.jpg.html" target="_blank">http://i135.photobucket.com/albums/q125/PursuitSS/Bolt%20Carriers/23031DC5-5EB3-4B3F-8A14-D43C31451924.jpg</a> I saw one on the EE not too long ago. Guy wanted like $250 for it. 
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Posted: 7/30/2016 2:06:13 AM EDT
[#26]
Curious myself.
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Posted: 7/30/2016 3:03:47 AM EDT
[#27]
All I remember is that the Hive Mind hated these gas tubes.
Doesn't sound like anyone here really knows. If someone tested it and had scientific results, I think the same people would contest the results, credibility of tester, and it would spiral out into nothing but baseless claims and personal attacks. I'd love to know, as a victim of a market with nothing but over gassed guns. Really don't want to spend the money on an LMT enhanced to make one gun right either. Molon, test these gas tubes! 
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Posted: 7/30/2016 9:49:00 AM EDT
[#28]
Quote HistoryQuoted:
I saw one on the EE not too long ago. Guy wanted like $250 for it. Quote HistoryQuoted:
Quoted:
IIRC, it was an attempt to TRY and achieve the same results that Tim LaFrance did with his patented "Twin Tube Gas System" that he designed for his M-16k By ALL reports, the M-16k was extremely reliable. <a href="http://s135.photobucket.com/user/PursuitSS/media/Bolt%20Carriers/23031DC5-5EB3-4B3F-8A14-D43C31451924.jpg.html" target="_blank">http://i135.photobucket.com/albums/q125/PursuitSS/Bolt%20Carriers/23031DC5-5EB3-4B3F-8A14-D43C31451924.jpg</a> I saw one on the EE not too long ago. Guy wanted like $250 for it. Damn, KNS has them on their web site for $150.00 |
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Posted: 7/31/2016 12:49:41 AM EDT
[#29]
I have a 16" carbine gas barrel that I bought new in '04. It had about 8,000 rounds through it when it started cycling hard enough to break parts, in 2012. Ejection was at about 12:30, almost straight forward. I figured it was gas port erosion. I saw no loss of accuracy (don't know about muzzle velocity, I don't have a chrono) so instead of replacing the barrel I installed a 9mm buffer and a fatboy gastube. It hasn't seen the same use since then, only about 1,000 rounds, but ejection is at 4:00 with m193. No cycling issues and no broken parts.
These things work but if you're having gas issues bad enough to warrant their use, you're probably better off replacing your barrel. You can almost buy a decent barrel for what some of them cost anyway. |
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Posted: 8/2/2016 4:09:19 PM EDT
[#30]
My brother had one of these in an Oly arms pistol upper. We all understand the theory behind them so when it broke eventually and he couldn't find another one he installed an adjustable block and a straight tube. With the block wide open that thing was violent and would have broken parts in short order. Tuning it down made it considerably more civil to run and didn't require any heavier buffer.
When it was running the pig tail it cycled fine until it broke. |
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Posted: 8/2/2016 8:05:22 PM EDT
[#31]
Quote HistoryQuoted:
It doesn't change the physical location of the gas port on the barrel.The entire tube is filled with air, no matter how long it is, as soon as you blow in one end air comes out the other end. it is not like you are dropping a single pellet in the tube and waiting for it to come out the other side, it is a column of air. That effect could only be true with a solid link, like a gas piston. It doesn't matter how long it is - it's a solid piece, so the back end moves at the same time the front end does. With a pigtail or 'fatboy' DI gas tube, it would take longer for the gas to build sufficient pressure to do it's work because the gas is compressible. The longer the gas tube, the longer the interval between the shot and the bolt opening, exactly the same effect as a longer distance from the gas port to the bolt on a regular mid-length or rifle. I think these modified gas tubes are rather eloquent solutions for getting less violent bolt carrier operation while retaining basically the same gun. |
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