Reader Donald writes:
The one concern I have building [a bolt carrier group] myself is staking the gas key. I have seen a guy on Youtube do it with a $80 dollar tool but was hoping not to have to buy anymore tools for this build. What’s your thought? Can I stake it with common tools like a center punch or should I try and find a gunsmith to do it for a fee?
So, for the uninitiated, two questions here. First, what does it mean to “stake” the gas key, and what does it do? And second, is it a DIY kind of thing? . . .
The AR-15 bolt carrier has a protrusion along the top called a “gas key.” During the firing sequence, this gas key accepts the hot gasses that have been bled from the barrel and redirects them into the piston chamber area of the bolt, causing the bolt to unlock and forcing the bolt carrier group backwards cycling the action. It’s an essential part of the operating system and needs to be flush with the bolt carrier surface in order to keep the gas from escaping before it can pressurize the piston.
The AR-15 BCG was designed in a time when forming things on a lathe was all the rage, and CNC machines were still a distant pipe dream. Which leads to the cylindrical design of all the AR-15 parts. It makes lathe machining easier. This also means that the bolt needs to be rather circular, so something like the gas key would need to be added later.
The gas key is held in place using a pair of screws set into the part. These screws need to stay tight in order to keep the bolt carrier together and keep the spice gas flowing. Unfortunately, one of the problems with using screws on a part that moves back and forth very quickly is that they tend to work themselves free after a while. And once they work themselves free, they can cause malfunctions and other issues in your gun. In other words, bad news.
How do you keep those screws from coming free? The answer is a practice called “staking.”
The idea is that you permanently deform the outer material surrounding the screws to apply increased friction to the screw heads. It allows you to still remove the screws if necessary (with the application of plenty of force) but keeps the screws from working themselves free under normal wear and tear. In theory, at least.
In practice, it doesn’t always work. My pre-1994 DPMS upper receiver has seen some heavy use, and the gas key is starting to work itself loose despite the gas key being staked. It’s gotten to the point where I just give the screws a good torque after every range trip just to be sure. However, if the screws weren’t staked, the wiggle would have been much worse and it would have happened sooner.
The best option is to ask a friendly gunsmith very nicely to help a brother out. The process takes all of five minutes, and since they should be all setup with vices and punches and a large hammer already, it won’t be a burden. Even if they want $40 for the pleasure, I’d lean towards handing over the cash for a professional job. Sure, you could eyeball it with a screwdriver and a large hammer, but (A) you’re going to bash the crap out of your anodizing which will lead to rust and (B) it won’t be as effective. Either buy the $80 tool, or pay a gunsmith.
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$80 tool? When I ran a company arms room, we used a hammer and a center punch. After I left active duty, I got a punch from Home Depot for about $5 that does the same thing, and it works fine. A screwdriver is certainly the wrong tool, but I don’t believe you need to break the bank, either.
As a Direct-Gas-Impingement aficionado, a flat-head screw driver would and has worked. The squared off shape is well suited to the task. I also used a diamond stone and took a punch down to be more stout and angular, almost like a chisel. That worked well.
It’s designed to puke in its own mouth. Anything more sophisticated than a stick and a rock are overkill.
The DGI system is an elegant design. It uses the bolt itself as the piston as opposed to a moving parts assembly. It is lighter, and inherantly accurate. It comes with one caveat; it needs to run wet. If you can handle that then you can take advantage of that which the system has to offer and have an extremely reliable weapon. If you can’t, then there is nothing wrong with grabbing a piston gun.
However, as the owner of both the SCAR 17 weapon system as well as an LMT MWS I can say this: my LMT laughs all the way to that 1,000 yard steel gong while my SCAR’s accuracy disintegrates between 6-800. And none of my LMTs (5.56 and 7.62) have malfunctioned. Ever. Just sayin’
Why not just clean the threads with brake cleaner and use a thread locker like Loctite?
Because the part gets hot.
To be more specific, during extended shooting the gas key gets above the temperature at which even high-temp red Loctite gives up. This is one of those cases where a mechanical solution (staking) is superior to “better living through chemistry”.
I’ve never spent that much time throwing rounds down a ‘poodle popper’ to pull out the IR and measure.
Does it really get that hot on something less than full-auto?
Gonna knock the AR as a poodle popper, but no idea that even a single shot heats up ridiculously fast. Lord
I would assume there is no chemical means–some kind of thread-locker–that would do the job?
Loc-tite stops working past a certain temperature, depending on the type. Not a great choice for this application.
Ahh. I see. Thanks.
2422 and 2620 are both good to 650F…
Rockset will work I`m sure , though I would have to think
getting them out if you ever have to , would be a bitch .
“keep the spice gas flowing.”
Not the first “Dune” reference on TTAG and certainly not the last. Nick, I genuinely appreciate them and your unashamed nerdiness. Well-armed and well-provisioned nerds shall inherit the earth.
+1
Walk without rhythm, and you won’t attract the worm.
“The Spice must flow”
Star Wars….
There’s no green text here…
“I must not fear.
Fear is the mind-killer.
Fear is the little-death that brings total obliteration.
I will face my fear.
I will permit it to pass over me and through me.
And when it has gone past i will turn the inner eye to see its path.
Where the fear has gone there will be nothing…… Only I will remain”
Appropriate in this time of pending threats to the 2A, no?
Ah, happy memories from my childhood.
I’ve heard too many animals complain as of late. It is good to see these references amongst the armed intelligentsia.
Dune reference FTW!
My local gunsmith has all the same vices I do… bourbon, cigars, gun porn. He does have a couple of vises I’d like to have.
Red loctite is only good until about 500 F (I thought the same thing until I read the datasheet). True there are epoxies and resins out there that would easily meet the temp requirement, but there’s a potential for having to deal with VOCs during mixing. Punches will give you a lot less cancer.
Good article, I would add that a quick gas key check should be part of your cleaning routine. Try to twist the gas key side to side and up an down with moderate pressure.
If nothing moves you are set to go.
Is there not a “Loctite” threadlocking adhesive that could substitute or this rather primative method?
Having worked for a department of 3000 sworn ( just about everyone had an AR) and built AR for years I have seen this issue. But by the same token the cause was usually the carrier was not staked well enough at the factory.
I’d weld before I would trust loc-tite in an application like this. Staking is easy and effective.
Thank you Foghorn!
Young Manufacturing (who makes some of the finest AR bolts you can buy) does not stake their gas keys because they do not feel it is necessary. they dont seem to have a problem
Young instead seals the base of the key & screw threads with Permatex. (something also required by Mil Spec yet no one else seems to do)
Yeah, and hardly anyone tourqes the key bolts as well, except Young, Les B, and myself. Les and I discussed this about 3 years ago, after asking him what he thought about Young. He said they are the Best in The Buisness of Carriers, thats why he used them!!
Which Permatex? That’s a company name, not a product.
^This. My Young Manufacturing BCG doesn’t have staked keys and runs like a champ. Haven’t had a problem yet and if you do stake the keys on a Young BCG you void the warranty. So ill be leaving it the way it came from Young.
As a Dune geek, I approve of that not so subtlety hidden reference. And i’ll leave this here: http://www.youtube.com/watch?v=21w60AU8NzA
Ive bin building AR’s since the early 1980’s. I do not STAKE gas keys, the reasons are it can loosen the allen bolt, or crack the screw head. I use red lock tight to adhere the key to the carrier, be carefull not to clog vent holes. Then install the key, here’s the trick..Tourqe the key bolts to 52 inch lbs..Make sure you clean surfaces and bolts with Breakfree Powder Blast well before starting. Young Manufacturing has bin doing this since 1995, with no issues. My uppers run like sewing machines with M16 lowers. You wont have any issues. Never reuse gas key, bolts, once tourqed, use new ones. 52 inch lbs is the max those bolts can take at one time. I have never had a gas key break, loosen or fail in over 1 million rounds since 1982!!
Red is the ‘killer app’ for auto parts that will see more abuse in one minute than any AR will see in 10 lifetimes.
“Staking’ is for things that are not precise and never need to be removed. Nor actively cycle. It’s a primitive ancient solution to problems that are far better solved with 19th and 20th century tech. Let alone 21st.
Your missing the point, if you tourqe the screws to 52 inch lbs they wont ever back out, the loc tite aids in the vibration. The tourqe keeps the bolts down, just like tourqing your lug bolts to 80 foot lbs on your truck, no one does it till they warp a rotor or break a lug.. Young runs his full auto till the gas tube glows like a torch, hes never had a gas key come loose.
Well I’ve seen unstaked gas key screws back out from regular use. Sounds like 16V is too good for such a “primitive” thing as staking the gas screws, but for the rest of us it is a simple and effective solution to keep them from backing out, and I fail to see the downside of it.
Bolt cutter will create a nice stake, just don’t rush.
I have built a few AR rifles in my time but I’m no ones gun smith, nor have I ever completed an AR centric armorer’s course. With that being said, every BCG I have ever purchased had a staked gas key. I have had to replace exactly one gas key ever. It was because a round blew a primer and (believe it or not) and it got lodged in the gas key. The gas key was quite simple to remove and didn’t take much force to remove the gas key bolts. I believe that had that gas key not been staked, it would have loosened at some point and caused an issue. I have no way of knowing if the gas key bolts were torqued to the required 52 inch pounds. If nothing else, staking the gas key will give me piece of mind, even after I torque the bolts to the required 52 inch pounds and use red locktite
I really wish people would stop with the archaic practice of staking. If you want to do it, fine but stop telling noobs it is necessary. 56 inch of torque and red loctite is far better than bashing metal together.
I read these comments and some buffoon always has to chime in on his uninformed ‘properly staking’ advice. Go to young manufacturing to see more.
Red or blue Loctite or the expensive green bearing seal Loctite will lock those screws in as good as or better than staking will. Staking is not foolproof anyway. I put some green Japanese thread locking compound on the Allen head shoulder bolts, ran them in at 55 inch pounds using a Utica torque wrench, and put I two small dimple marks per screw using a Klein all metal awl on one gun and just used the green Japan made thread locking compound on another gun. The staked key actually started to leak. The impact from staking likely broke the Japanese version of Loc Tite free. The mating surfaces were lightly coated with Permatex 80008 #1 or slow drying #2 gasket dressing sealer. My father was a diehard original gray goo Permatex fan. After many many hours spent scraping Permatex off of gasket surfaces, I prefer Hylomar blue now. It is some sort of a super magical non-silicon blue goo sh** that Rolls Royce uses on their jet engines and it just works like a dream. It doesn’t EVER harden but it won’t blow out either. You clean it up with brake parts cleaner and a rag. Even after 4 or 5 or 10 years stuck to a water pump gasket, it just wipes off. Cylinder heads? Yes! Exhaust manifolds? Maybe not, I never tried it. Gas keys? No problems. So I am okay with either Permatex or Hylomar. Those surfaces are small enough it’s not that much scraping, say compared to a timing chain cover or both the heads on a V8. My dad had an old Colt 600 series. Those gas keys were staked on with a simple hammer & a punch. I put some of that green Jap thread lock on a large fan blade center nut. It took a lot of beating on a big wrench with a bigger hammer to get that sucker backed off again. It was bad enough, I’d rather risk it unscrewing itself and taking out the radiator. It’s fine for gas key bolts! They ain’t coming out!