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

AR-15 Staked Castle Nut - thearmsguide.com

January 7, 2021 by Nate Schultz (nsz85) 20 Comments

Staking Your AR-15 Castle Nut

Why is staking a castle nut so important? Why can’t I use blue thread lock?” That is something people often ask me about building an AR-15. I have found that a large number of people with whom I have spoken do not realize the importance of staking the castle nut on their AR-15. 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 - thearmsguide.com
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 buffer tube nut, is a circular, 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 designed explicitly for staking purposes.

Why Stake Your Castle Nut

Not staking the castle nut on your AR-15 is taking quite a considerable 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 endplate 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 to prevent your bolt from fully seating, which can make a round go off inside the receiver but not in the chamber. That is especially true with AR-15 style bolt carriers instead of M-16 bolt carriers because of the typical lightning 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 them that something catastrophic will likely not have convenient timing. Why take the chance and allow the dangerous possibility of that catastrophic failure? You don’t want your AR-15’s stock to fall off.

How to Stake Your Castle Nut

AR-15 Staked Castle Nut - thearmsguide.com
Notice how I am manipulating material from the receiver end plate into the small notch on the castle nut. Staking is that easy.

You can avoid all of this trouble by taking roughly 60 seconds to stake your castle nut properly. Follow these simple steps:

  1. Make sure that you have correctly installed your castle nut 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 endplate into one (or two) of the small notches on the castle nut. That will render the castle nut properly staked and semi-permanent.

Check out our list of the best buffers for your AR-15.

Filed Under: AR-15

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About the Author

Avatar for Nate Schultz (nsz85)

Nate Schultz (nsz85) 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: www.youtube.com/nsz85

See All Nate Schultz (nsz85) Articles

Comments

  1. Avatar for Nate Schultz (nsz85)Nate Schultz says

    October 27, 2013 at 11:49 pm

    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.

    Reply
  2. Avatar for Nate Schultz (nsz85)1tyme says

    October 28, 2013 at 11:48 am

    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.

    Reply
  3. Avatar for Nate Schultz (nsz85)cwoods3 says

    October 29, 2013 at 6:53 pm

    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?

    Reply
  4. Avatar for Nate Schultz (nsz85)Nate Schultz says

    October 29, 2013 at 7:06 pm

    Page 0025-8. I took a screen shot for you. I hope this helps. http://i.imgur.com/Nia4gT2.jpg

    Reply
  5. Avatar for Nate Schultz (nsz85)cwoods3 says

    October 29, 2013 at 7:25 pm

    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.

    Reply
  6. Avatar for Nate Schultz (nsz85)Nate Schultz says

    October 29, 2013 at 7:56 pm

    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. 🙂

    Reply
  7. Avatar for Nate Schultz (nsz85)FateofDestinee says

    November 7, 2013 at 8:55 pm

    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. >.>

    Reply
  8. Avatar for Nate Schultz (nsz85)tgace says

    December 31, 2013 at 9:39 am

    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? 

    Yeah..you are that guy…

    🙂

    Reply
  9. Avatar for Nate Schultz (nsz85)MKLII says

    May 29, 2014 at 11:00 pm

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

    Reply
  10. Avatar for Nate Schultz (nsz85)TXCOMT says

    February 24, 2016 at 9:23 pm

    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!

    Reply
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