How do I change an AR gas tube?

[Patrick L]

I just bought a new gas tube system for my 20 year old HBAR. I figured 20 years of carbon build up etc. was enough. It didn't come with instructions. How does one go about changing the gas tube? It looks like just drive out the roll pin, put in the new tube, and replace the roll pin, right?

It also has the piece that goes on top of the bolt carrier. Is there a torque specification for that, or just good and tight? Do I really need to change that?

It's not that I'm not handy, its just that I'm not up on these plastic guns. Walnut and steel are what I know. Any help would be appreciated.

[boltaction308]

I would NOT change the piece on the bolt carrier, it has to be staked down and unless it is badly worn on the inside, there is no need.

As far as the gas tube, you are correct, just drive out the roll pin, make sure the gas tube is in right side up, then put the pin back up.
Its a lot easier if you take the front sight/gas block off the barrel first but this may not be required depending on the individual setup.

[rockrat]

Pulled a number of gas tubes off without taking off the front sight.

Just drive out the roll pin (be careful, they are easy to lose), then pull the tube to the rear and move it to either side of the front sight, then pull forward and out. You might have to twist it a bit either way to get it to move. Unless the part on top of the bolt is damaged, don't bother with it. If loose, then re-tighten the screws and re-stake them in place.

You could get one of the gas tube cleaners, looks like a long pipe cleaner, and run thru your gas tube and see if it is clogged up in any way. Possibly put some carb cleaner on it, to clean out the carbon, ect. You might not have to change your gas tube.

[tomme boy]

If it doesn't have a hole in it, leave the tube alone. Keep the new tube and pin ( you did get a new pin right? ) as a spare.

[jrayborn]

Unless you have shot the barrel smooth, there is very likely no reason at all to change the gas tube. I second the notion to keep the new tube as a spare.

[Patrick L]

Well, nearly 20 years of shooting with the original tube seems like it may be time to swap it out. Don't they get carboned up? I've never done a thing to it.

[tomme boy]

Nope, leave it alone. If it was carboned up, your gun would not be cycling the next round. I change out the gas rings on the bolt every once in awhile but that is about it. You should always have a spare set of rings and pivot. I really like the one piece rings. They are really tight at first.

[nhrifle]

There is no significant fouling build up in the gas tube of an AR. Every time a round goes off, ignition gas is blasted through to the bolt carrier at substantial velocity, not allowing it to stick to the tube. All that carbon does collect inside the receiver though in the form of all the black nastiness that gets wiped off the bolt carrier and out of the upper receiver. Leave the tube alone as they don't generally fail unless they are crushed or bent from external damage. Of course, if you got it hot enough, you could possibly melt a hole into it.

[Patrick L]

What got me thinking all this was that I started playing with cast in the AR. I'm concentrating on IMR 4895 since I have so much of it. In reading other's posts, everyone seems to be getting theirs to function using @19 - 19.5 gr with a 55 - 60 gr boolit. I need to get up to around 23 gr for the rifle to function. I keep it clean everywhere else, so I was thinking that maybe the tube was staring to choke off.

Am I totally off base in my reasoning?

[tomme boy]

When was the last time you changed the gas rings?

Is this a carbine or rifle? If carbine, what buffer is being used?

[Patrick L]

Full length rifle.

Never changed rings. Rifle always functioned fine with factory or equivalent jacketed handloads. Did replace bolt(whole assy complete w/rings) about a year ago, but only because it had corroded on tail end. Still functioned fine, just ugly.

[vernm]

The part on top of the bolt carrier is the gas key. You may have gas leakage between the gas key and the bolt carrier.
If you see evidence of gas escape around the base of the key or the key is loose, torque to 80 inch pounds and stake.
Do a Google search for gas key staking and you will have plenty of instructions.

As stated before, worn gas rings can cause the rifle to be "under gassed". Yours are fairly new. Hold the carrier with bolt installed. Then tip the front straight down. If the bolt falls out or moves, you may need new rings.

Unless you have a specific reason, I would not change out the gas tube. Most need to be changed because someone got one of those long pipe cleaners stuck in the tube. The tube cleans itself. Don't worry about it.

[tomme boy]

What carrier do you have? Semi auto, M16?? Post a pic showing the whole thing from the side. Need to see the bottom rear portion. If it is the heavy M16, that might be your problem. The lightweight carriers should work the best in the AR's shooting cast. You could also get a lighter weight recoil spring.

[tomme boy]

You know I was just thinking. You might have a smaller gas port than most. Since the Obama scare started, the gas ports have been on the large side. QC has gone down a lot. That might be why your needs a little more to make it work. Yours is actually in spec where it is supposed to be.

[dkf]

Can't you just clean up the gas tube some with a few long pipe cleaners and some solvent?

[Mk42gunner]

I add my vote to leaving the gas tube alone.

However, if you decide to go ahead and change it anyway, soak the forward end with kroil for a few days prior to attempting to pull the tube. Just about every tube I saw changed on M16-A2E3's when I ran the armory for NMCB-5 broke where it was drilled for the retaining pin. Getting the forward portion out was always a PITA.

Robert

[tomme boy]

Heat it up with a torch and then spray it with oil till it stops burning off. The oil will suck in. Also use a pair of vice grips to try to twist it first. But like everyone keeps telling you. Leave it alone. It self cleans itself.

[nhrifle]

Also, I've never seen it happen, but I have heard stories of the gas tube pipe cleaners getting stuck inside the tubes and then you have to replace it.

[GabbyM]

You'll want to make sure your locking lugs up in the barrel extension are nice and clean. For ease of unlock.
You can also have gas leakage around the front sight block to barrel fit.

[Patrick L]

Well, you guys have convinced me, I guess I'll just leave it be and keep the new one as a spare. I don't wqnt to change springs, as I do still shoot factory and j boolit handloads.

[cheese1566]

Also, I've never seen it happen, but I have heard stories of the gas tube pipe cleaners getting stuck inside the tubes and then you have to replace it.

Exactly! I was taught by one of the best AR armorer instructors to never place anything in the gas tube or the tube on top of the bolt carrier. They will not plug as they have "lots" of pressure going through them...enough to work the action.

[GabbyM]

There's been piles of hoey spread out by outfits trying to make sales on gas piston variations of AR's.
Seams suddenly after fifty years of dependable service AR's don't work anymore.

[DCM]

What carrier do you have? Semi auto, M16?? Post a pic showing the whole thing from the side. Need to see the bottom rear portion. If it is the heavy M16, that might be your problem. The lightweight carriers should work the best in the AR's shooting cast. You could also get a lighter weight recoil spring.

+1 on that.

[Mk42gunner]

Also, I've never seen it happen, but I have heard stories of the gas tube pipe cleaners getting stuck inside the tubes and then you have to replace it.

I have. Even worse were the 6" wooden Q-tips that got broken off; you can occasionally got the pipe cleaners out, but the wooden swab usually meant a new gas tube and lots of cussing by the armorer.


Exactly! I was taught by one of the best AR armorer instructors to never place anything in the gas tube or the tube on top of the bolt carrier. They will not plug as they have "lots" of pressure going through them...enough to work the action.

Most thinking people hear "Don't stick anything in the gas tube" and think "Maybe I shouldn't do that." Not Seabee's, they seemed to delight in making more work for us armorers.

Robert

[Nickle]

All because the buffer needed to be changed (it was) and Winchester had too much calcium carbonate in the powder (they didn't know before, and they fixed that too).

I've had few problems with IMR powder. I'm fond of 4895, but do use ball powder too.

[GabbyM]

That calcium carbonate was added to the ball powder in WWII to reduce muzzle flash from the M1. Since the Japanese were quite adept at returning fire upon the flash. McNamara’s whiz kids, Donald Rumsfeld being one, chose to use the old stockpile WWII powder instead of the proper new powder. To save money. Modern ball powder does not contain calcium carbonate. I get better accuracy from the stick powders in 223 but do have good results and velocity from Ramshot TAC with 55 gr bullets. The old M1 ball powder also burned slower than the IMR used in the original USAG AR-15's. causing high port pressure and faster cycling rates. They moved gas port forwards I believe. Plus the buffer change to get the guns slowed down. And of course started chrome plating the chambers so cases wouldn't rust in place overnight. deletion of the chrome plating was another of the Whiz Kids big ideas. Back shortly before the whiz kids some geniuses in the USAF decided they didn't need a gun on a fighter plane and built the F4 with no gun. From my perspective, which may be flawed, things have only became worse. Like the M4 with a pistol length barrel.

My cast boolit 223 load using H-4198 burns extremely clean. If anything I could use it to clean out carbon fouling after shooting the full power J bullet TAC loads. Which are dirty. Any bullet lube that ran down the gas tube should IMHO only serve to soften carbon fouling to help blow it on out just like lube in BP guns.

Back in the 1970’s I bought into that gas tube fouling sausage. Made up a funnel with rubber tube that slipped over the end of the gas tube. Pour solvent in funnel to run down tube. Used a strap clamp to hold upper to bench muzzle down with jar under muzzle to recover solvent. Waste of time. However one could use this method to check for gas tube blockade if you were concerned. If solvent runs through quickly you’re good to go. Right? You can even plug your flash hider, not bore muzzle, and pour the barrel and tube full of solvent to soak. Need to be careful what solvent you use. Any ammonia and you’ll frost your bore with a long soak time.

[Nickle]

The 5.56 powder was WC 846, not the WC 852 from .30 caliber M2 Ball. 852 is way too slow for the AR. There's more to it. And, it'd slot of info. Read "The Black Rifle". It isn't cheap, but is very enlightening.

The powder was all wrong, and they hedged their way around the problem.

Chrome lining the chamber and bore wasn't done to the M16 because they hadn't figured out how to chrome line a 22 centerfire at that time. Yes McNamara's idiots weren't pushing the issue either, they would shout down anybody that argued the AR-15 wasn't fully wrung out yet. Even Eugene Stoner said it wasn't fully debugged yet. But, the hate for the National Armory system was in full force. They especially had it in for Springfield Armory.

Now, my opinion of Donald Rumsfeld isn't good, nor will I state it here. This is a polite family friendly forum, and the moderators would take exception to the language required to adequately state my thoughts. I leave it that he's a waste of skin, and consumes perfectly good air. And not fit to flip burgers at McDonald's. I think shoveling manure is too high tech for him. Yeah, that bad.