View Full Version : Worn out Gas Tubes
I think I've stumbled upon my 3rd worn out gas tube. By worn out I mean on the carrier key end where there's a larger diameter band that seals in the carrier key.
A few years back I had two mid-length BCM tubes that wore down on that area to the point where the gas leakage cause soft/short stroking. I have a BCM SOCOM Carbine factory upper that's several years old. It has always been excessively soft on bolt speed/cycling, but I could never figure out why. I even dropped down to a carbine H2 buffer system from the A5 Vltor to improve cycling.
Yesterday I went to clean this gun (which I recently started shooting more often) and noticed the gas tube has no visible step up in diameter on the end that sticks into the gas key.
This would be my 3rd BCM gas tube from 5+ years ago that has failed prematurely. None of these had excessive firing schedules at all.
(Anyone know who has Colt carbine gas tubes in stock?) Brownells and Arms Unlimited are out of stock.
Yeah, there isn't much Colt stock anywhere right now. Sorry I can't help you, but as a potential alternative, you might give a Wilson Combat gas tube a shot.
In case you didn't know, there is a guage for that measurement, if you're at all curious.
Mark Brown Custom Gas Tube Gauge (https://www.brownells.com/tools-cleaning/gun-tools/rifle-tools/ar-15m16-gas-tube-gauge/)
I'm interested in pulling the tube an measuring it, but I don't want to be stuck with no replacement for months. The gun does run good, but the tube finally explains the sluggish bolt speed I'd noticed for years.
I'm interested in pulling the tube an measuring it, but I don't want to be stuck with no replacement for months. The gun does run good, but the tube finally explains the sluggish bolt speed I'd noticed for years.
That guage allows you to measure it in the upper Mark. I check mine every time I clean them. I'm guessing this is more of a thing than most of us realize, otherwise that gauge woudln't exist. Interesting you posted your observations on this topic.
I'm too cheap to buy the gauge, but I could see it being handy. Usually I look for that shiny band around the tube where no fouling has accumulated... just a rough visual check.
Someone posted the diameter measurements here years ago.
Maybe the inside of the gas key is rough? Maybe a nitrided tube would last longer?
Hey Mark,
Replacement tubes are here:
https://blackrivertactical.com/WP/Gas-System-c6464008
Maybe the inside of the gas key is rough? Maybe a nitrided tube would last longer?
Either that, a tight inner diameter, or a slight misalignment would be my guesses. @markm, you could check for misalignment by sliding the BCG onto the gas tube (with the upper off the lower) and see if you see or feel any significant difference is resistance compared to other uppers. If it turns out to be the gas key, you could either get the carrier rekeyed, or use one the carriers off your spare BCGs.
Good points above, if you have a set of pin gauges, you can check the inside diameter of your gas key.
G = .180
Y = .181
R = .182
Maybe the inside of the gas key is rough? Maybe a nitrided tube would last longer?
Nitrided tubes do last longer here, and would be something I'd look at for sure.
Going though several tubes sounds gas key related, likely alignment but who knows.
To check strip the carrier down and slide it back and forth to check to contact with the tube... if it's strong and moves the tube at all you've got an issue and you should bend it a little. Hold the upper muzzle down and drop the empty carrier and make sure it bounces (doesn't work assembled with the bolt in).
Maybe the inside of the gas key is rough? Maybe a nitrided tube would last longer?
I though that on the first one. But after 3 bad tubes (all different guns), I'm speculating that there were some tubes with soft steel a few years back.
Hey Mark,
Replacement tubes are here:
https://blackrivertactical.com/WP/Gas-System-c6464008
Thanks!
Either that, a tight inner diameter, or a slight misalignment would be my guesses. @markm, you could check for misalignment by sliding the BCG onto the gas tube (with the upper off the lower) and see if you see or feel any significant difference is resistance compared to other uppers. If it turns out to be the gas key, you could either get the carrier rekeyed, or use one the carriers off your spare BCGs.
I generally check that with all my guns, and I definitely was checking this on the first two after replacing the bad tubes. The replacements haven't given me any problems.
Going though several tubes sounds gas key related, likely alignment but who knows.
3 different guns/BGGs. I had suspicions that there were bad tubes, and I thought it was only mid-length, but this 3rd gun in carbine exceeds the coincidence threshold on the problem.
It's not been that uncommon for me to see tubes that need to be replaced. Not something I see regularly, but often enough it doesn't surprise me anymore. At this point, I think Murphy strikes more often than most people give him credit for. While giving PMI a few years ago, I was explaining that joes should check for loose gas keys during cleaning, and the random rifle I used for the demonstration had a loose gas key.
It's not been that uncommon for me to see tubes that need to be replaced.
Most modern rail/handguards cover up the tube in front of the receiver (unlike the old delta rings). On my first bad tube, I could have figured out the problem sooner, but all the leaking gas fouling was hidden under the rail.
There are several ways to check the gas tube alignment.
A slightly misaligned gas tube can cause premature ware.
Specialized Armament has Colt gas tubes. Not sure if you are willing to wait a month to get them though?
Specialized Armament has Colt gas tubes. Not sure if you are willing to wait a month to get them though?
Nah. I ordered a pair from BRT.
Here's the bad one:
https://i.imgur.com/FZIy3jX.jpg
That's a smooth operator...
Nah. I ordered a pair from BRT.
Here's the bad one:
https://i.imgur.com/FZIy3jX.jpg
Nah. I ordered a pair from BRT.
Crap, I forgot that G&R has Colt gas tubes too.
I had one get eroded at the port and start giving me malfunctions.
I replaced it with a BRT tube.
There are several ways to check the gas tube alignment.
A slightly misaligned gas tube can cause premature ware.
Not that I do not believe you, but how can a misaligned tube cause premature wear? I would think that misaligned would imply that it is impeding some of the gas flow?
Not that I do not believe you, but how can a misaligned tube cause premature wear? I would think that misaligned would imply that it is impeding some of the gas flow?He's referring to the alignment between the tube and gas key, not the tube and port on the barrel.
Yeah. That'll rub one side smooth probably. These bad tube have no "step up" on the full circumference of the tube. Gas is just bleeding out of the key.
Dang dude, you don't need no guage to tell those are bad! I suspect your suspicions are correct on those tubes, that looks pretty bad to my eyes.
I've had one gas tube wear out in the same way as Mark's. It was on an upper I had built back in '09 that wore out the bulb on the tube in under 5k rounds. Replaced it with something better, don't remember what but maybe a DD tube, and I think I've got at least 5k additional on that upper with the new tube. Haven't looked at it recently, but I think I'll pull it out of the safe and give it a cleaning and once over.
Not that I do not believe you, but how can a misaligned tube cause premature wear? I would think that misaligned would imply that it is impeding some of the gas flow?
georgeib correctly explained what what I was referring to.
I've had one gas tube wear out in the same way as Mark's. It was on an upper I had built back in '09 that wore out the bulb on the tube in under 5k rounds. Replaced it with something better, don't remember what but maybe a DD tube, and I think I've got at least 5k additional on that upper with the new tube. Haven't looked at it recently, but I think I'll pull it out of the safe and give it a cleaning and once over.
I really don't pay too much attention to this, but if I clean a gun I'll take a peek. I pulled this tube yesterday and it had caked on fouling right about the area of the barrel nut. If this were a middy, I'd probably have figured it out sooner because I thought the middy tubes were the problem.
I can't wait to shoot this gun with a new tube. I remember running a suppressor on this thing years ago and thinking how well it was gassed. Now I know why it's weak with no can and good with a suppressor.
Thank you for reminding me ( us ) about gas tube wear.
I would have forgotten to consider this as a function issue.
Sometimes I tend to forget these simple fixes.
Sorry if I missed it, and not that it matters, did you happen to have a approximate round count ?
Sorry if I missed it, and not that it matters, did you happen to have a approximate round count ?
Best guess is a couple thousand. I've had the upper for many years, but it was not shot much and kept as a hedge on supply issues/bans, etc. You can tell by the pic that the upper hasn't seen a lot of rounds through it.
ViniVidivici
10-19-23, 14:58
This is why I keep round counts on everything, in a maintenance log, so I know if something is wearing out earlier than it should, and when it's time to proactively change things.
This is why I keep round counts on everything, in a maintenance log, so I know if something is wearing out earlier than it should, and when it's time to proactively change things.
I'm terrible at keeping that kind of information. Even worse with chrono info. I can't count the number of times I've had to retest some powder lot that I was certain, I wouldn't forget.
New BRT tube is in. Dial Calipers indicate a .010" difference between the new and old tube.
I went and looked at my BCM 11.5 upper after reading this thread. Round count is 2,100. Sure enough, bulb on gas tube is almost worn smooth. I’ve never had a malfunction with this upper, but I ordered a BRT gas tube to go ahead and replace it. I have higher round count Colts with no perceivable wear on the gas tube. This BCM upper was purchased 11/2018
New BRT tube is in. Dial Calipers indicate a .010" difference between the new and old tube.
Please report back after you've tried it out and let us know what you think.
triggerjerk
10-22-23, 12:29
Is that extra . 010 at the bulb/gas key end or in the main tube diameter (as in tighter fit/less leak at gas block)?
Ned Christiansen
10-22-23, 14:37
Gonna sorta quote myself from my AR class.
If you wanted to make the perfect tool for wearing out gas tube ends you'd make a carrier key that was rough in the bore and then chrome it for hardness. Mfgrs tend to skip things like ream and hone when they can get away with it or when there's a buying surge on. I've seen some really rough ones. Have also had students complain of carriers that eat gas rings, same deal, quality reduced in the name of increased production and profits, rough-assed bore when the rings ride. "DROP THE HONING OPERATION, WE HAVE ORDERS TO FILL!"
Gas tubes being long and flexible, and carriers having a certain amount of slop in the upper, and with cheezy set-screwed-on low pro gas blocks that can be installed in not exactly the right orientation, yes, it's pretty easy to get misalignment. I have students remove the bolt and test for interference. Put the carrier alone in horizontally so gravity is not pushing you from behind in your careful testing. Little finger in the back of the carrier, push it in gently several times, biasing it up, down, left, right. You are almost certain to feel or hear some kind of contact but as long as it's not actual interference, you should be good. Of course this has to be with a not-worn gas tube end. If you are getting interference, your gas tube's life will be shortened. Sounds crude but bend it if you have to! I do it all the time. Eventually you will have to change the GT anyway; test all over again.
New tube pictured below with the correctly visible band where the tube seals in the key. The carbine carbine ran very noticeably better. Solid cycling and ejection with .223 pressure 77 gr loads.
On Ned's note, I'll monitor this tube for premature wear and explore key replacement if the problem repeats.
https://i.imgur.com/FVWMWLw.jpg
the AR-15 Junkie
10-23-23, 06:44
I went and looked at my BCM 11.5 upper after reading this thread. Round count is 2,100. Sure enough, bulb on gas tube is almost worn smooth. I’ve never had a malfunction with this upper, but I ordered a BRT gas tube to go ahead and replace it. I have higher round count Colts with no perceivable wear on the gas tube. This BCM upper was purchased 11/2018
Did you check the top of the tube between tube and upper receiver? You have to remove the gas tube to see that side of it, or buy the MBC tool if you have a lot of guns to check.
Gonna sorta quote myself from my AR class.
If you wanted to make the perfect tool for wearing out gas tube ends you'd make a carrier key that was rough in the bore and then chrome it for hardness. Mfgrs tend to skip things like ream and hone when they can get away with it or when there's a buying surge on. I've seen some really rough ones. Have also had students complain of carriers that eat gas rings, same deal, quality reduced in the name of increased production and profits, rough-assed bore when the rings ride. "DROP THE HONING OPERATION, WE HAVE ORDERS TO FILL!"
Gas tubes being long and flexible, and carriers having a certain amount of slop in the upper, and with cheezy set-screwed-on low pro gas blocks that can be installed in not exactly the right orientation, yes, it's pretty easy to get misalignment. I have students remove the bolt and test for interference. Put the carrier alone in horizontally so gravity is not pushing you from behind in your careful testing. Little finger in the back of the carrier, push it in gently several times, biasing it up, down, left, right. You are almost certain to feel or hear some kind of contact but as long as it's not actual interference, you should be good. Of course this has to be with a not-worn gas tube end. If you are getting interference, your gas tube's life will be shortened. Sounds crude but bend it if you have to! I do it all the time. Eventually you will have to change the GT anyway; test all over again.
Hey Ned, what happened to your site? It's not pulling up for me.
the AR-15 Junkie
10-24-23, 08:07
Hey Ned, what happened to your site? It's not pulling up for me.
http://www.m-guns.com/
works for me.
http://www.m-guns.com/
works for me.
This is what I get when I click on the link. > https://www.wm7d.net/
This is what I get when I click on the link. > https://www.wm7d.net/
Same here. Are you using a VPN?
http://www.m-guns.com/
works for me.
This appears to be on a shared IP address. www.m-guns.com takes me to the Michiguns Ltd page with an IP address of 192.153.5.149 -- if I enter that IP directly I get a page for Estate Sporting Limited.
Same here. Are you using a VPN?
I had to check (no computer tech whizz), but apparently so... Still never had issues getting to the m-guns site until yesterday though.
the AR-15 Junkie
10-24-23, 18:26
I had to check (no computer tech whizz), but apparently so... Still never had issues getting to the m-guns site until yesterday though.
Just checked, still working correct for me.
Just checked, still working correct for me.
I was able to get there on my phone just now, which I wasn't able to earlier today. Still can't get there through my laptop, but I haven't turned the VPN off.
Edit: Tried turning VPN off and it didn't change anything for me.
titsonritz
10-24-23, 19:54
Ned’s site works fine for me for whatever that is worth.
I was able to get there on my phone just now, which I wasn't able to earlier today. Still can't get there through my laptop, but I haven't turned the VPN off.
Edit: Tried turning VPN off and it didn't change anything for me.It's got to be a DNS thing. You're probably still using the same DNS servers with and without the VPN.
It's got to be a DNS thing. You're probably still using the same DNS servers with and without the VPN.
Very well could be. No idea on my end being as technologically challenged as I am. I'm figuring that something must have changed in an automatic update at some point since I haven't had problems getting to Ned's site throughout the year until recently.
It's got to be a DNS thing. You're probably still using the same DNS servers with and without the VPN.
I think so too. A problem with the shared IP address, and since it is shared you cannot put in the IP address to visit the site.
I caused an under gassed KAC upper that ended up being a gas tube in the same condition described. The ‘bulb’ was worn off.
I was very surprised to see this. This upper had one variable. It had been through a couple days worth of carbine class in a very sandy range. It was a deep mid to fine beach sand brought in to cover the range.
We did a lot of drills that got a lot of sand in the action. I remember cleaning it out of up where the gas tube was and the BCG being covered. The sand had stuck to the lube and made an abrasive compound.
We did a lot of drills that got a lot of sand in the action. I remember cleaning it out of up where the gas tube was and the BCG being covered. The sand had stuck to the lube and made an abrasive compound.
Another good reason to use a nitrided gas tube it seems.
Each time I've had this happen I've run a q-tip into the key to check for obvious rough surfaces. My old thought was that there was some bad/soft gas keys a few years back, but maybe Ned's notion of slightly rough/non-honed keys is the issue.
Another good reason to use a nitrided gas tube it seems.
I'd rather replace a gas tube than a gas key.
I'd rather replace a gas tube than a gas key.
Yeah. I trust almost nothing nitride/melonite. American Mediocrity has polluted that process too. We had first hand experience with a shit faxon barrel.
I'd rather replace a gas tube than a gas key.
The key is already chrome lined. Are you supposing a smooth QPQ finish would damage that?
The key is already chrome lined. Are you supposing a smooth QPQ finish would damage that?If the goal, as you implied, to using a melonited gas tube is to decrease wear of the tube, then the wear is by necessity being transferred to the gas key. Though hard chrome is still significantly harder (~69 RC) than a melonited stainless gas tube (43-52 RC), the melonited tube will still wear the chrome. As will a standard gas tube, though at a significantly slower rate.
At the end of the day, I would rather wear out gas tubes than gas keys. I have one or two melonited gas tubes in a parts pin somewhere around here. I removed them, in part, because I realized that if they were of real advantage, they would have likely been specced long ago.
I removed them, in part, because I realized that of they were of real advantage, they would have likely been specced long ago.
This! Much like the crap the SpringCo makes. If it was needed, it would have been a requirement.
the AR-15 Junkie
11-01-23, 11:17
This! Much like the crap the SpringCo makes. If it was needed, it would have been a requirement.
Agree 100%
Agree 100%
They've made a fortune selling nonsense/snake oil. Maybe Pfizer will buy them as a subsidiary. :jester:
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