What’s At Stake
Short Story: If you want to build correctly and safely, you must stake your gas key and castle nut.
What Is Staking?
Staking in this context means displacement of metal between two parts, such that those two parts are locked in place relative to one another. Typically, one part will have notches cut out, into which material from the other part is displaced using a punch.
Why Stake?
Staking ensures that two parts don’t move, relative to one another. This is typically important for parts that NEED to stay put. If those parts move, bad things happen.
What Parts Should Be Staked and Why?
Gas Key and Gas Key Screws
Short Story: Properly staking your gas key will keep it from peeling off of the bolt carrier, mid-cycle.
The most important part to stake is the gas key. These gas key screws secure the gas key to the bolt carrier.
The gas key experiences a humongous amount of stress as the pressurized gas impinges into the hollow key and flows into the bolt carrier. This pressure drives the reciprocating mass (bolt carrier group and buffer) to the rear of the firearm, thereby cycling the spent case out of the upper receiver. This is a lot of force on a small area. If the gas key screws begin to back out, a lot of bad things can happen: damage to the bolt carrier/gas key/gas key screws, pressurized gas escaping into the upper receiver too early, insufficient blowback to cycle the gun, and if the screws snap, a big friggin’ mess in your gun.
Once the gas key is installed on the bolt carrier and the gas key screws are torqued to the appropriate level, material on the gas key is staked inward on the edge of the screw holes (typically in two places per screw), which deforms some of the metal on the gas key into contact with the knurled head of the gas key screw. The metal holds the gas key screw in place, relative to the gas key so that the screws cannot back out over time. The image below shows a properly staked gas key.
If you are purchasing an assembled bolt carrier group or a bolt carrier with the gas key already installed, the gas key is probably already properly staked, as this is the Mil-Spec standard. The manufacturer’s description should indicate if the gas key is staked.
If you are assembling a bolt carrier group from individual parts, or you have to replace the gas key for any reason, you will need to stake (or re-stake) the gas key. You can accomplish this with a metal punch and hammer (see our Tools and Materials page for more), but both Brownells$ and Michiguns make a purpose-built tool that makes this process easy if you will be doing this frequently.
Receiver Extension End Plate and Castle Nut
Short Story: Properly staking your castle nut will keep your stock and receiver extension from rotating while in use.
The receiver extension assembly on an AR carbine or pistol is comprised of the receiver extension (or buffer tube), the receiver extension end plate, and the receiver extension castle nut (or lock nut). The receiver extension houses the buffer and buffer spring, and for carbines, the buttstock slides over the receiver extension.
The castle nut has notches in both sides. One set (the four larger cutouts) is for the castle nut wrench. The other set (the three smaller notches) are for staking.
Once the receiver extension is threaded into the lower receiver, the end plate is pressed against the lower receiver and the castle nut is threaded forward and torqued. Once torqued appropriately, material on the end plate is deformed into the notches cut into the front face of the castle nut. This locks the castle nut in place, preventing it from loosening. The image below shows a properly-staked castle nut.
The consequences of not staking the castle nut and end plate are nowhere near as severe as with the gas key and gas key screws; you won’t get sudden catastrophic failure.
If the castle nut loosens, your receiver extension will not be secure in the threads of the lower receiver. Vibration during normal use can cause damage to the threads in the lower receiver or receiver extension.
If you are not using a receiver extension with anti-rotation tabs, you could have bigger issues. With the castle nut loosened, the receiver extension can now rotate in the lower receiver threads. For a carbine, the rotation of the receiver extension will be apparent, as the stock will begin to rotate with the receiver extension (most people will notice if their stock rotates 90 degrees…). For a pistol, the rotation of the receiver extension will be less apparent and, therefore, can be more of a problem. As the receiver extension backs out of the lower receiver threads, the following will occur (in sequence):
- As the edge of the receiver extension moves to the rear, the buffer retainer pin will no longer be held into the applicable cavity. The pin and spring will pop up and be free to roam about the interior of the AR. These can get jammed anywhere from the receiver extension to the chamber, and everywhere in between.
- If, by chance, you either aren’t using a buffer retainer pin (e.g. if you are using a captured buffer spring), you will begin to experience cycling issues, as the reciprocating mass will have more room to reciprocate.
- As the receiver extension threads are on their last bit of contact with the lower receiver, the receiver extension may tear out of the lower receiver threads, thereby damaging the threads on both parts.
- Finally, if your receiver happens to pop off in the middle of a firing sequence, the buffer, buffer spring, and bolt carrier could go flying out of the gun and, most importantly, you could get hurt.
Unless you buy a pre-assembled (i.e. complete) lower receiver, you will need to stake your castle nut. If you replace your receiver extension, end plate, or castle nut, you will need to re-stake the castle nut. It is not a hard thing to do, so we recommend that you do it.
Staking Is Not Forever
Just because you stake a part does not mean that it cannot be removed. You will need to put a little more oomf into removing the part than if it wasn’t staked, but you probably won’t have an issue. As you unscrew the gas key screw or castle nut, the deformed metal from the opposing part will be pushed out of the way.
If you remove a staked component for any reason, be sure to re-stake it once it is reinstalled and re-torqued.
Thread Locker Is Not A Substitute For Staking
Some uninformed folks will tell you that thread locker is a perfectly acceptable substitute for staking (and even torquing). If you are tempted to believe this, don’t (visit our Lock and Lube article for more). Suffice to say, DO NOT USE THREAD LOCKER IN PLACE OF STAKING.