I’m constantly amazed at the number of people who believe that the gas impingement system of the AR-15 rifle and M4 carbine is somehow a liability. So strong is this belief that there is today a growing subset of the industry making good money by adding parts to the original Stoner design in a misguided attempt to “fix” the “problems”.
Over the years (and many tens of thousands of rounds) I’ve not found the gas system of the AR pattern rifles to be of any kind of issue. Mike Pannone recently wrote a good article about the misconceptions surrounding the gas impingement system, and his long term test to prove them wrong, over at Defense Review. I recommend that you read the article, as his observations generally mirror mine (with the exception that I’ve not found it necessary to modify my Colt Carbine, which has proven completely reliable in the nearly 20 years I’ve owned it.)
Many complaints about the gas system concern the reputed tendency of the gas tube to clog, which I don’t doubt has occasionally happened. The way to avoid that is to never clean the gas tube!
Lots of shooters will put bore cleaner down the gas tube and swab with one of the gas tube brushes available. This is the start of the problem, as you can never completely swab out the cleaner. As soon as hot gases are introduced during the firing cycle the remaining petroleum turns to carbon and adheres to the walls of the gas tube. Repeated cleanings simply add to the deposits.
When I get a new rifle I take a gas tube brush and use acetone or denatured alcohol (acetone works better) to clean out any oils from the gas tube, then I never touch it again! You can run a brush down the tubes on my rifles and it will come out clean. The gas tube is designed to be self cleaning, and as long as you don’t soil it yourself it will do its job.
At the other end of the tube, where the gas contacts the bolt carrier to drive it during recoil, is the other source of misplaced concern: that the gas system fouls the bolt and causes stoppages (“it defecates where it eats” is the nonsensical refrain, usually stated a bit more colorfully than I have.) I’ve never found this to be a problem either, and again it comes down to proper maintenance.
Many people are of the impression that the gas relief holes in the bolt carrier are for oiling the bolt. Resist that temptation! Oil down those holes gets into the gas rings and onto the back side of the bolt, where the hot gases quickly turn the oil into carbonized sludge.
I prefer to lubricate the bolt head in front of the gas rings, on the little ridge that runs around the bolt head and serves as a contact point in the bolt carrier. I prefer to use a light, non-tackified grease (food grade NLGI #0, such as Lubriplate SFL) on just that ring as well as on the locking lugs themselves. There’s no need to lube the rings or any surface on the back end of the bolt.
A little of that same grease on the contact rails of the bolt carrier and you’re done. The AR-15 bolt assembly needs lubrication to function, but doesn’t need to be dripping wet.
How reliable are my rifles with this regimen? A couple of years ago I spent several dry, dusty days at a range in Fernley, NV. The earth from which the range was carved was not sandy; it was very much like talcum powder. The dust got into everything (including the pores of the green plastic furniture on one of my guns, which to this day I’ve not been able to thoroughly remove.) During that time several of the guns malfunctioned, including a SIG 550 (or is it a 556? I can never remember their nomenclature.)
Both of my rifles ran without any attention, to the point that several other participants preferred to borrow my guns rather than trust theirs when time for the end-of-course shooting contest came around.
The direct impingement gas system is as reliable as any other when understood and maintained appropriately. I’ve not found it necessary to be anal retentive in doing so, either; I don’t spend a lot of time cleaning them, because most of the parts are self-cleaning by design unless you do something to mess them up. Learn how the system works, understand where the contact points are and make sure they’re lubricated, and your AR-15 will likely work as well as mine do.
-=[ Grant ]=-