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.