I notice that there isn’t an entry for an ID of .120 in the chart posted by UCRT. Significant? I’m not knowledgeable enough to say.
Those are hypodermic tubing gauges. http://www.connhypo.com/pages/sub05_toc01.html
My searching has yielded nothing but questions. I saw someone post that his search fu was not working. I think my fu may have been foo’d by his…
Regardless, the only thing I found was that the TDP is “not available on the internet.”. Is there a way I can find this data?
And FYI, I’m now on an info quest, this is not about “where to buy” a gas tube:-)
Thanks all, for the good discussion.
HA HA HA! Hate to say it, but…
Spike’s beat them to it this time. They have a melonite treated gas tube that they use on their 5.45 mm upper receivers.
It’s a pretty good idea for corrosive ammo, actually.
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I think it is quite possible that some type of hypodermic tubing might be what an AR uses…but that is just speculation.
Generally, a designer will try to use what is already available unless there is some unique set of circumstances that requires a special design, which raises the price. For a Gas Tube to sell for $10, it can’t be too exotic.
I’ve seen this commonality of parts on 20k+ hp motors; axial, recip, & centrifugal compressors; gas turbines; steam turbines; etc. I’d reckon there isn’t a “special” diameter for AR’s, just a spec for a certain temperature and pressure but again…speculation.
FWIW
Here’s a LINK to McMaster-Carr’s catalog page about hypodermic tubing.
But maybe it’s just me…
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Titanium doesn’t always make everything better by default. Seems the gas tube is very low on Murphy’s list, hence the difficulty in finding a reoccurring method of failure where the gas tube was the primary cause. It’s probably why manufacturers have left it alone.
I use BCM or Colt so I don’t have to do research on who’s gas tube is GTG.
edit @ucrt
was thinking more like http://plymouth.na4.acrobat.com/stainlessspecs/
Since AR was an aircraft company and the wall sizes are closer.
It was sarcastic 
Mostly. It also has better heat tolerance. If I was trying to think of a fast way to make AR more reliable in full auto I would say open bolt.
I have got to see this. Could you post the link since i can not find it on their websit.
I’ve only seen it complete with the 5.45 upper…the entire thing is treated with Melonite…AIM sells them…