Published on October 20th, 2013 | by Nate Schultz (nsz85)

AR-15 How To Tips: Stake Your Castle Nut in 3 Easy Steps

“Why is staking a castle nut so important? Why can’t I just use blue thread lock?” This is something I am regularly asked about building an AR-15. I have found that a large number of people with whom I have spoken do not realize the importance behind staking the castle nut on their AR-15. Personally, I am a big proponent for staking a castle nut and will always do it on any AR-15 variant that I build for myself or others.

What is a Castle Nut

AR-15 Staked Castle Nut -

These are two examples of stakes that I have done with a spring loaded center punch.

But let’s back up a minute, what is the “castle nut” and what does it do? A castle nut, also referred to as a receiver extension nut, is a circular and notched nut that screws onto the AR-15 lower receiver extension (buffer tube) and keeps the receiver extension and lower receiver end plate secured in place. On a standard mil-spec castle nut, one side will have large notches that look like little squares have been cut out of it (hence the nickname because it resembles the top of a castle tower). On the other side, there are smaller notches or indents which should be facing the receiver end plate when correctly installed. These smaller notches are there and have been specifically designed for staking purposes.

Why Stake Your Castle Nut

Not staking the castle nut on your AR-15 is taking quite a large risk. Many people, myself included, own an AR-15 for self-defense purposes because of its proven reliability and accuracy. By not staking your castle nut, you reduce the overall reliability of your AR-15 and, in turn, introduce a higher probability of a catastrophic failure.

Take a moment and consider the following scenario. Say you chose not to stake the castle nut on your AR-15, and after some range time, the castle nut becomes loose. That causes the end plate to become loose. Once the end plate is loose, the takedown pin spring and detent can fall out. Now, the receiver extension can move, which means it will no longer hold the buffer retainer in place, so your buffer and buffer spring can’t stay in place. All of this can happen in just a second or after few shots without you even noticing. That is, until either your AR-15 explodes or the receiver extension breaks apart—both of which would render your AR-15 completely inoperable.

“My AR-15 could explode? Ha, that’s doubtful.” Not necessarily. All it takes is for the buffer retainer to become trapped somewhere in the upper receiver as to not allow for your bolt to fully seat which will lead to a round being fired while not inside the chamber. This is especially true with AR-15 style bolt carriers instead of M-16 bolt carriers because of the typical lightening cut.

Many have told me that they “have used blue thread lock on the castle nut and have never had a problem in all their years of shooting AR-15s.” My response to them is to remind that something catastrophic will likely not have convenient timing. Why take the chance and allow the dangerous possibility of that catastrophic failure?

How to Stake Your Castle Nut

AR-15 Staked Castle Nut -

Notice how I am manipulating material from the receiver end plate into the small notch on the castle nut. Staking is that easy.

All of this trouble can be easily avoided by taking roughly 60 seconds to properly stake your castle nut. Watch my video above and follow these simple steps:

1. Make sure that your castle nut is properly installed at 40 foot pounds of torque on the receiver extension with the small notches facing the receiver end plate.
2. Using either a spring loaded center punch or a standard center punch and a hammer, place the tip of the punch onto the lower receiver end plate that is in line with a small staking notch on the castle nut.
3. Using force, manipulate enough material from the end plate into one (or two) of the small notches on the castle nut. This will then render the castle nut properly staked and semi-permanent. (To learn how to remove a staked castle nut, you may watch my other video by clicking here.)

About the Author

Nate Schultz is employed within the field of Law Enforcement, is an avid shooter, firearms enthusiast and hobbiest gunsmith. When he is not writing for The Arms Guide, he is producing content for his YouTube channel:

  • CK5150

    Interesting and informative-I didn’t know about that procedure before.  Plus it’s just funny to hear someone say castle nut.  Kind of like urinal cake.  Just sounds funny.

  • 1tyme

    It happened to me on my first Bushmaster. My buffer spring sheared off my detent and I didn’t even know. This was due to too much play in the buffer tube. My Colt is staked beautifully and is good to go.

  • 1tyme

    It happened to me on my first Bushmaster. My buffer spring sheared off my detent and I didn’t even know. This was due to too much play in the buffer tube. My Colt is staked beautifully and is good to go.

  • BamaG

    Thanks for this info! I am new to the AR scene, and recently added a sling plate to my AR. I didn’t know the staking was this important. Looks like I’ve got some staking to do…

  • drmorris9

    Do you have a good technique for Gas key staking?  My last BCG has somewhat anemic staking.  I attempted to push a little more material, but found the key was nearly as hard as my punch, and I didn’t accomplish much.  I am sure my technique is to blame.

  • 1tyme

    I’ve heard they use a special peening hammer on gas keys. My Colt came staked pretty tight so I’ve never done a key job.

  • I believe you are correct. In fact, I think there is some type of press involved with some manufacturers. I have always known BCM as having the best stake jobs on keys.

  • I have not had to fix any stakes on my gas keys at all. If I found myself with a loose one, I would more than likely send it back to the manufacturer to get fixed.

  • Congrats on your new AR! If you ever have any questions, please feel free to contact me 🙂

  • Perfect example and I am glad that your experience was mild. I have heard of much worse and to think it could have been avoided by taking 60 seconds to stake the castle nut.

  • Ha, well I am glad I was able to be informational as well as entertaining. 😛

  • BamaG

    Nate Schultz Much appreciated!

  • cwoods3

    Okay, I’ll be that guy. I have been shooting AR platforms for over 18 years (Military/LE/ civilian), not once have I ever had a problem with a castle nut coming loose. If people who do not have training or experience with working on these guns would just leave things alone, there would not be a reason to “fix” it. All of these weapons come from the factory tuned and tightened to the proper specs. Did you really use a window punch to demonstrate this? Can’t emphasize this enough-proper training and tools. Some things (gas keys) need to be staked, others (castle nuts) don’t.

  • Staking the castle nut twice is per the manual and is per mil-spec. I am not sure what you are referencing to claim that it doesn’t need to be staked. Please enlighten me.

  • 1tyme

    When my Bushmaster had the castle nut problem I ended up switching out buttstocks. Our department armorer put the new one on and staked it. I’ve since sold that weapon and bought a 6920 with a Rogers stock. The castle nut on that one came staked straight from Colt.

  • cwoods3

    Nate Schultz 
    I understand that many manufactureres are staking their castle nuts at the factory now. Thats great, it keeps people from screwing with them. In looking at Army FM’s and TM’s that I have, I can’t find where it mandates staking the castle nut. What do you mean by “Mil Spec”? Being a veteran, to me, that only means that a given item will function properly “most of the time”. Also, in consulting the other armorers that I work with, staking can be done, but it is a field expediant fix if the castle nut is worn to the point it won’t hold any torque. What manual are you referencing?

  • Page 0025-8. I took a screen shot for you. I hope this helps.

  • cwoods3

    Nate Schultz 
    Apparently, that is a newer version of TM that I have. However, I still don’t think that it is necassary. And I also believe that it is irresponsible to tell people that their rifle is going to explode if they don’t do it.
    It wans’t covered in any of my armorer schools, and no one that I spoke with about it thinks it has to be done.

  • I can tell that this topic is really important to you and I am happy that you were able to learn something from my article. 🙂

  • Stake it! Stake it, before dusk falls and its power grows to great to control!
    …I may need to cut back on re-reading Dracula. >.>

  • tgace

    cwoods3 Window punch, center punch, whatever…as long as it moves a little bit of metal into the staking slot (what… you thought those notches on the Castle Nut were decorative?) does it really matter what type of punch he used? are that guy…



    Had one come loose over the weekend. Where’s my center punch….?


    Latecomer to this party, but let me say the post is greatly appreciated! While my new SSK12 Minuteman from Midwest Industries came with a staked castle nut, my other entry-level ARs did not. Sooo, I made a trip to Lowe’s and got a General automatic punch and am taking care of business! Thanks again!

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