AR-15 Gas System Maintenance
BY Herschel Smith
5 years, 1 month ago
Direct-impingement (DI) gas tubes—such as those used on most AR platforms—should be checked periodically to ensure the hardware that secures them is present and tightly fitted. If you can access that area, removing the roll pin (or screw) will allow you to inspect the forward end of the gas tube for any cracks where the pin passes through. This is not a frequent check, but it is worth doing anytime you remove a gas tube. Any cracking around the pin hole requires replacement of the tube. Remember to re-pin the gas tube after reinserting it into the block.
Gas tubes benefit from periodic internal cleaning, too. Short, large-diameter AK- and SKS-style gas tubes can be scrubbed out with an appropriately sized brush and solvent, then swabbed dry with a clean, lint-free rag. Ensure that the locking cam that holds your gas tube in place remains fully engaged when assembled and that the tube itself is not badly dented or misshapen.
AR-type tubes can be cleaned out with long, purpose-made pipe cleaners and some bore solvent or a .063- to .076-diameter spring wire. You can do this from inside the upper receiver, eliminating the excuse of not wanting to remove the gas tube. Judging by past comments I have received on this subject previously, the concept of cleaning gas tubes is taboo in some circles. As long as you do not stick something in there that will get stuck (like the end of a cotton swab) cleaning it out is both acceptable and recommended. Use a flashlight if the dark space scares you. Just clean it out and move along, little fella. Check gas-tube ends for damage from moving parts, such as bolt-carrier keys or locking cams. Replace the tube if it has been beaten up in this area.
I’ve never cleaned gas tubes, and I’d like some gunsmiths to weigh in with their experience with this. Is this really necessary? The gas velocity in the tube is extremely high.
On November 4, 2019 at 11:00 pm, Houston said:
Grant Cunningham says Never Ever put any solvent or carbon based cleaner in the gas tube. He says when you get a new gun clean once with acetone and then leave it alone. Anything else you put in the tube will cause it to accumilate carbon deposits. I’ve followed this and never had an issue.
On November 4, 2019 at 11:05 pm, Houston said:
Grant also says DO NOT put oil in the two holes in the side of the bolt carrier. That is not what they are meant for and don’t need oil in the gas changer of the carrier.
On November 5, 2019 at 9:58 am, George said:
I am not a gunsmith but I was an armorer. Where I worked, gas tubes were never serviced just to clean them. I never saw an issue with a gas tube being blocked causing the weapon to not cycle.
For my personal AR about once a year I will stand the upper up with the muzzle down and spray some brake cleaner in the tube (the non-chlorine type). I allow the cleaner to work a little and then use compressed air to blow it out. I have been doing this for many years and have never had a gas tube issue. I am not sure this procedure is needed though. It is just my habit.
I have found that, especially for new weapons, the most important thing with gas tubes is to make sure they are properly aligned with the bolt carrier. With no lube a stripped carrier should pass the 45 degree test. Put the stripped carrier in the upper about half way. Then tilt the upper so the carrier will fall toward the chamber. If the gas tube is close to acceptable alignment it should fall completely forward at something less than or equal to 45 degrees.
If you get more than a very minimal resistance ( a slight click) when the gas key is accepting the end of the tube then the gas tube needs to be adjusted, that is, bent slightly to ensure minimal resistance to going into the gas key. There is a special tool you can purchase to do this.
Over the years I have bought a few gas tubes that came bent. It is not uncommon. The stripped carrier should actually rattle a little bit when it is all the way forward in the upper. The carrier assembly in an AR 15 is designed to be sort of free floating with relation to the gas tube. If it is too tight it will affect the accuracy of the weapon.
On November 5, 2019 at 10:10 am, Jack said:
This could be answered with a borescope. Unfortunately, sub 3mm borescopes are prohibitivly expensive
If I had the time, I’d mill the side off of a sacrificial gas tube… Since I don’t have the time, I’ll throw $20 towards the project if someone else volunteers….
On November 5, 2019 at 10:14 am, Herschel Smith said:
@George,
I like the idea of compressed air. Good for many, many things. Not so sure I like the idea of brake cleaner. Have to ponder that one.
@Jack,
Ha! Um, no thanks.
On November 5, 2019 at 10:56 am, Fred said:
Not a gunsmith but there might be two difference circumstances. To further characterize the question; in one instance would be recreational and hunting use or in the other is when a man really needs it. Occasional cleaning of your baby might be one thing but what of a primary battle rifle?
On November 5, 2019 at 12:12 pm, Frank Clarke said:
I tried to clean it with a Q-Tip once and long regretted it until I could get the debris out. Pipe cleaners seem to work OK, but very little seems to accumulate and need cleaning there in any case. I’m thinking ‘every year or so’?
On November 5, 2019 at 12:59 pm, Bill Sullivan said:
I have not done this with an AR, but I have cleaned a stuck gas piston on an M-1 carbine by filling the bore with carburetor cleaner. It will eat through a carbon clog, and start leaking out around the gas piston. Pretty quick (5 minutes or so), the gas piston slides freely. A little compressed air- or “canned air” for cleaning keyboards- will dry it all very quickly.
On November 5, 2019 at 1:07 pm, MTHead said:
At the shop, (just down the road from a gun range), I saw hundreds of AR’s in every condition one can imagine. Never anything in the gas tube.
Hershel’s spot on. It gets a 50,000psi. clearing blast every time you pull the trigger.
Lucas Botkin, (T-Rex arms), Had over 12,000rnds. of Wolf through his 13.7″ gun. No plugs.
And before I would try to clean one, I would just replace it. $20.00, and 20mins. worth you and your families life?
On November 5, 2019 at 4:13 pm, Bill said:
MTHead for the win.
On November 5, 2019 at 6:29 pm, Matt said:
I’ll second MTHead. If you have a gas tube issue it’s easier to simply replace it and be done with it.