View Full Version : Proactive measures to prevent gas leaks
Steve_in_Allentown
08-28-21, 15:13
I spent a decade behind an M16 buttstock courtesy of Uncle Sugar so while I know which end is the dangerous one and I can field strip it, I do not have an intimate knowledge of its inner workings. To alleviate my ignorance in this area I've collected all the necessary bits and pieces to put together my first upper.
The Aero gas block slips easily over the ARP barrel boss. It is not a press fit. I'm looking for tried and true methods to prevent gas from leaking out from between these two parts.
Same question for the gas tube and the gas block.
Inkslinger
08-28-21, 15:16
Install correctly. Shoot the gun and carbon buildup will do the rest.
We prefer the tried and true method of using a better quality gas block with a much closer fit that minimizes gas leaks in the first place.
Green Loctite, if you don't expect to remove it?
I use the Loc-Tite 290 (green) for bedding gas blocks. To get it to work well degrease the barrel gas block, bbl, set screws with BreakFree Powder Blast or Gunscrubber.
If you ever have to disassemble you'll need a good heatgun and a plastic/rawhide hammer to remove it.
Pinning a gas block is always a good idea. With that said, I feel that if you install a clamp GB (the way we do it) and the GB is sitting under a rail, it will never come loose.
We first degrease the barrel and GB. We then put green loctite on the gas port area. The GB screws are then degreased coated with rocksett and then torqued on with 50-60 inch lbs.
We have NEVER had a GB come loose or ever even shift on ANY weapon we have done.
Green loctite works well. I would argue that I could green loctite a GB (read no set screws or pins) and it would never move. How do I know? Once in a while I have the mis-fortune of having to remove a GB that I installed. :(
Good to know on the bedding for barrels. I use green Loctite 620 sleeve retainer between the gas block and barrel for an absurd fit and a semi permanent installation.
ViniVidivici
08-28-21, 17:03
I've got an Aero GB on one gun. It's just fine.
If the measurements match (as in, both .750, etc.) don't worry too much about it, as others have said, it will "self seal".
And think about it.....as the screws and/or pin comes into play, it does kind of force the GB down against the barrel in the gas port area.
BufordTJustice
08-28-21, 17:13
Green Loctite, if you don't expect to remove it?
Correct.
You would have to press it off, likely with a healthy amount of heat.
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Install correctly. Shoot the gun and carbon buildup will do the rest.
This. Does not need a 'press fit' and nothing wrong with Aero quality.
Green Loctite, if you don't expect to remove it?
Correct.
You would have to press it off, likely with a healthy amount of heat.
That's not how green Loctite works. Green Loctite is designed for parts that are a press or close fit that will be later removed for repairs or replacement. It has good capillary (wicking) action to fill the tiny imperfections between close or press fit parts to create a good non-permanent bond seal between two surfaces.
Green Loctite is perfect for sealing gas block installations.
BufordTJustice
08-28-21, 21:43
That's not how green Loctite works. Green Loctite is designed for parts that are a press or close fit that will be later removed for repairs or replacement. It has good capillary (wicking) action to fill the tiny imperfections between close or press fit parts to create a good non-permanent bond seal between two surfaces.
Green Loctite is perfect for sealing gas block installations.
There's 290 and 620. 290 is a thin, wicking liquid for pre-assembled fasteners. 620 is a viscous liquid, designed to be a sleeve retainer.
I have and use both. But my comments were referring to 620 sleeve retainer. That's what I use on gas block journals.
Also, it's been a while. Hope you're well, Mist.
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We prefer the tried and true method of using a better quality gas block with a much closer fit that minimizes gas leaks in the first place.
^^This^^
There's 290 and 620. 290 is a thin, wicking liquid for pre-assembled fasteners. 620 is a viscous liquid, designed to be a sleeve retainer.
I have and use both. But my comments were referring to 620 sleeve retainer. That's what I use on gas block journals.
Also, it's been a while. Hope you're well, Mist.
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How hot does a gas block get? Looks like 620 is good to about 400 degrees. I know red Loctite is rendered useless after one heat cycle above what it likes. Does 620 react the same way?
BufordTJustice
08-29-21, 11:32
How hot does a gas block get? Looks like 620 is good to about 400 degrees. I know red Loctite is rendered useless after one heat cycle above what it likes. Does 620 react the same way?
Well there is more than one high temp red. One is a as you describe and the other isn't. The other turns gooey and still has torque retaining ability.
I haven't monitored gas Block temperatures. I'm sure they get high. I took this advice from Will way back when and it has served me extremely well. If, for no other reason, it promotes the immediate self-sealing between the gas block and the journal.
As Clint said, I *always* use tightly fitted gas blocks and barrels from high quality manufacturers. This isn't a fix for poor fitment.
So, by the time I get the barrel and gas block hot enough to really affect the sleeve retainer, I've got such a good gas seal from accumulation of fouling/combustion byproducts that I don't care.
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...it's been a while. Hope you're well, Mist.
It has, and I am. Good to see you again.
The point made about using a close fit gas block is a good one.
How hot does a gas block get?
From a long string of fire, it can get hot enough to sear skin.
Steam rising from a hot FSB
https://photos.smugmug.com/F1/AR-General/n-9HMHf7/i-hQw3dvq/0/7045829b/M/i-hQw3dvq-M.jpg
How hot does a gas block get? Looks like 620 is good to about 400 degrees. I know red Loctite is rendered useless after one heat cycle above what it likes. Does 620 react the same way?
Barrel temperature obviously is related to rate of fire.
The barrel, under the gas block can get to:
10 rounds per minute (1 round every 6 seconds), approximately 300 rounds = 375 to 390 degrees F. Given the slow temperature increase versus time, the gas block is probably in equilibrium.
One round every 3 seconds, , 300 rounds = 500 F
One round every second:
5 seconds - 275 F
10 seconds - 425 F
15 seconds - 550F
20 seconds - 625 F
25 seconds - 700 F
30 seconds - 750 F
One 30 round magazine dump will probably break down any Loctite.
Steve_in_Allentown
08-29-21, 17:31
Thanks everyone for your replies. Lots of good information. I appreciate everyone's time and effort to help me out.
If I didn't mention it earlier, the gas block is an Aero Precision and the barrel is an AR Performance. Taking another look at things today the block doesn't rattle around on the barrel. It's a close fit but not what I'd call an interference fit. It easily slides into place and the set screws snug it down nicely.
As long as it doesn't shoot loose you're not going to have leaks. You can pin it if it needs to be bombproof.
I don't know how hot gas blocks get, but I've used red loctite on the screws for installation for a while. Once I used a bit too much and it wicked down on the journal. Something I didn't find out until several months and probably a thousand rounds later. I will typically shoot 4 or 5 mags in a row from each rifle per session, and all the oil will cook off the barrel by the second mag - so it's safe to say I'm not afraid to get it hot.
Anyway, in trying to remove the gas block, I used heat - propane to heat the screws til they could be removed. The gas block still wouldn't budge. I suspected what happened and ended up heating with a propane torch for a full minute before still having to use a mallet to slide it off. With multiple blows at that.
Just wanted to share my one experience with red loctite as a sleeve retaining compound. Inadvertent as it was.
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