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Posted: 1/25/2006 8:51:07 AM EDT
I have an oly 7inches barrel ar, I've ever wondered what would be the real purpose of the shroud on the gas tube, here is a picture:



Anyone have some input or info?

Thanks
Link Posted: 1/25/2006 9:02:47 AM EDT
Well, I'm guessing, maybe shape retention. Extreme heating and cooling of metal does strange things. Especially tubing since their isn't much mass.
Link Posted: 1/25/2006 9:12:29 AM EDT

Originally Posted By AtLarge:
Well, I'm guessing, maybe shape retention. Extreme heating and cooling of metal does strange things. Especially tubing since their isn't much mass.



+1

I have seen someone use the pig tail gas tube before and it didn't work very well. It kept pulling out of the fsb when it heated up and breaking the pin that holds the tube in the fsb. Maybe it was just pulling it out of the upper, don't remember but it did split the hand guards appart.

My guess for the "shroud" is to keep the coil from twisting the tube and pulling it out of the fsb or upper. When the tube heats up it makes the coil expand and twist causing all kinds of problems. You may not see this only firing a few rounds at a time but full auto beta dumps is where you see the problem.
Link Posted: 1/25/2006 1:28:15 PM EDT
looks like he did that to keep it from drooping, looks like he gets that thing pretty hot.
Link Posted: 1/25/2006 1:29:13 PM EDT
[Last Edit: 1/25/2006 1:31:15 PM EDT by eklikwhoa]

Originally Posted By 5isalive:

Originally Posted By AtLarge:
Well, I'm guessing, maybe shape retention. Extreme heating and cooling of metal does strange things. Especially tubing since their isn't much mass.



+1

I have seen someone use the pig tail gas tube before and it didn't work very well. It kept pulling out of the fsb when it heated up and breaking the pin that holds the tube in the fsb. Maybe it was just pulling it out of the upper, don't remember but it did split the hand guards appart.

My guess for the "shroud" is to keep the coil from twisting the tube and pulling it out of the fsb or upper. When the tube heats up it makes the coil expand and twist causing all kinds of problems. You may not see this only firing a few rounds at a time but full auto beta dumps is where you see the problem.




sounds like he had other problems or a tube that wasnt correctly made. probably getting stuck in the carrier key/bolt carrier? dont really see how there could be that much movement in the pigtail to actually pull itself out of the fsb, the curved ends would get cocked in the gas tube hole, wouldnt it? i dont see much room for it to get pulled out but hey, what do i know?
Link Posted: 1/25/2006 2:07:12 PM EDT
[Last Edit: 1/25/2006 2:07:45 PM EDT by 5isalive]
Don't know for sure but this is what I think was happening. When the coil gets heated up it expands and pushes the tube into the fsb harder and harder. The gas going through the tube is pushing the tube out of the fsb and eventually the pin saws through the tube causeing the next round to push the tube completely out of the fsb.

I didn't get a very good look at it when it happened but was watching him fire. He was doing full auto on a beta mag and it was on the 2nd beta when the weapon failed to eject the spent case. He just pulled the charging handle loaded another round fired and that is when the handguards split in two. When he removed the guard that is when I seen the pigtail but I am not sure where it came apart. It is totally possible that the pin holding in the tube wasn't even there or had losened it self.
Link Posted: 1/25/2006 2:18:48 PM EDT
I have an AR pistol with a 7.5 inch Barrel.
(semi only)

My gas tube is straight from the gas block to the bolt.
I have no function problems - gas related or otherwise.

I can only guess that he uses the pigtail on the Full Auto to lower the gas pressure and thus the cyclic rate of the weapon.

So i would assume the bracket is just for securing the tube from movement.
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