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Discussion Starter #1 (Edited)
I've been planning on replacing the take-down pins in my MR556 lower with standard mil-spec pins. Why? Because I consider them a PITA and I hate having to get that little tool or a punch anytime I want to break the gun apart or get at the BCG. Well, tonight I got bored and swapped 'em out. I learned a few things in the process that I feel might be helpful to anyone attempting to do the same.

First, for those not familiar with front takedown pin removal/installation, here you go:
DIY AR-15 Build: Pivot Pin Installation

You will notice the installed milspec pin and the HK pin both have holes in them, but in different places:


To remove a milspec pin, the pin is pulled out and the hole in the pin body should line up with the detent/spring assembly. You insert a 1/16" punch and depress the detent/spring. You can then rotate the pin so that the so the detent does not extend into its respective channel in the back of the pin. The take down pin can now be removed easily. (NOTE: care should be taken as the detent and spring are under tension and are easily lost if not contained).

Notice in the pic that the HK takedown pin (the loose pin) does not have this hole in the body; rather, it is in the "head" (for lack of a better term) of the pin. This presents a bit of a problem since even if a punch is inserted and the detent/spring is depressed, the pin can not be rotated and removed due to the flat side of the pin head contacting the detent spring housing portion of the lower. What I did instead was to depress the detent/spring with my punch and shim a very thin feeler gauge between the pin head and housing, keeping the detent/spring captured in the housing. I could then pull the pin out and rotate it so the channel faced up. At this point I removed the shim and the takedown pin.


The rear takedown pin also presented a slight challenge. The castle nut on the receiver extension is staked. I simply used a small punch and a light hammer to "un-stake" the castle nut.



I have seen tutorials on other forums that advise using "cheater" bars and just muscling through this process. DO NOT DO THAT!!!! For the most part, there really is no good way to securely place an AR lower in a vice, apply great amounts of torque, AND not cause damage. If it is necessary (which it has yet to be for me), I would wrap the extension/buffer tube in leather and put that in a barrel clamp, and realize a new buffer tube may be a possibility. Since HK buffer tubes aren't cheap and or commonly in stock, I wanted to avoid this. I don't recommend the magazine style blocks for anything other than holding the lower in a workable position where no significant force is applied.

After I got as most of the staking material pushed back from the castle nut, I put on a pair of leather gloves. I gripped the buffer tube in one hand had my spanner wrench in the other. I was able to break the castle nut free. I recommend using a zip tie to keep the backplate from slipping on you and damaging your rear takedown pin spring. (NOTE: this spring is also under pressure and is easily lost) Since I was swapping out the rear pin, I only had to move the backplate enough to gain access to the spring. Take care when reinstalling the spring and back plate not to bind/break the spring.

RESULTS:
My rear pin was replaced with a new Colt pin, but as you can see form the wear on the front pin, I had to find a loaner from an LMT lower that isn't currently in use. I do have a slight amount of receiver play now, but it's no worse than standard AR receiver play. I will see if a new front takedown pin makes any difference. If accuracy suffers (which I doubt it will), I would consider reinstalling the front pin only, but leave the rear pin to allow quick/easy access to the BCG/upper internals.

UPDATE: The front pin was replace with a new Colt pivot pin. This helped to reduce the play slightly. While a slight amount of "play" still exists between the 416 upper and MR556 lower, it is significantly less than any of the factory Colt or LMT rifles that are in my possession or care. There has also been no loss or change in accuracy going between the HK to milspec pins (new or used).
 

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Don't know if u saw it ,the mag recoil it had a neat trick for securing the rear take down pin spring w a set screw , I was going to do it but just had my lgs do the slap plate swap for me
 

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Can we contact HK Customer Service and order the "non-tooled", "HK416", "Mil-Spec" takedown pins or do they need to be ordered from a HK parts distributor?
It seems like I read here before where someone provided the part numbers, cost and advised HK would sell them to you if you called.

TC
 

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Discussion Starter #5
Can we contact HK Customer Service and order the "non-tooled", "HK416", "Mil-Spec" takedown pins or do they need to be ordered from a HK parts distributor?
It seems like I read here before where someone provided the part numbers, cost and advised HK would sell them to you if you called.

TC
Why go through all that trouble and pay a premium for a set of takedown pins? I have faith in companies like Colt and LMT to make a suitable pin.
 

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The take down pin can now be removed easily. (NOTE: care should be taken as the detent and spring are under tension and are easily lost if not contained).
I made the mistake of accidently slipping my tool and the detent flew out of the lower receiver. I spent the next hour and a half on my knees with a flash light looking for a very small black pin in my darkish carpet, my wife thought it was funny, I was pretty upset.

My rear pin was replaced with a new Colt pin, but as you can see form the wear on the front pin, I had to find a loaner from an LMT lower that isn't currently in use. I do have a slight amount of receiver play now, but it's no worse than standard AR receiver play. I will see if a new front takedown pin makes any difference. If accuracy suffers (which I doubt it will), I would consider reinstalling the front pin only, but leave the rear pin to allow quick/easy access to the BCG/upper internals.
I went with YHM EZ Pull Takedown Pin Set and I have no receiver play, I am very pleased with these take down pins.

 

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No offense, but I can remove my HK pins in less than 20 seconds with the tool in the stock. Why does it need to be taken down quicker than that(not including combat duties)? A buddy of mine replaced his take down pins in his MR556 and now he has the typical upper/lower loose play that IMO less quality AR's exhibit.
 

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IMHO you should really never need a tool to take down a weapon, its an unnecessary step. I went with the EZ pull pins because I have big hands and it takes awhile to dig my nail and extract a pin in a normal AR platform. I have no idea why HK needed a locking mechanism in a take down pin, but its really unnecessary. I guess its on the operator and his preference.

If H&K was really in need to lock it, why not go with pins like that of a HK 9-series weapons, same affect, just no little tool to misplace and get lost.
 

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That makes sense.

I thought I read some where that HK used the pins to tighten up the upper and lower receiver.
 

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Discussion Starter #10
IMHO you should really never need a tool to take down a weapon, its an unnecessary step.
... no little tool to misplace and get lost.
BINGO!

Also, I don't use the HK stock or grip, so I don't have a convenient place to store that tool anymore. My grip stores a spare CR2032 and is glued shut (as ERGO's bottom likes to pop out over time). The SOPMOD does not lend itself to easy access either.

And yes, the ball detent applies tension to the upper and in a roundabout way reduces play due to the tension.
 

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I made the mistake of accidently slipping my tool and the detent flew out of the lower receiver. I spent the next hour and a half on my knees with a flash light looking for a very small black pin in my darkish carpet, my wife thought it was funny, I was pretty upset.



I went with YHM EZ Pull Takedown Pin Set and I have no receiver play, I am very pleased with these take down pins.

Hello i have installed tonight the pins, no play, very nice!

No offense, but I can remove my HK pins in less than 20 seconds with the tool in the stock. Why does it need to be taken down quicker than that(not including combat duties)? A buddy of mine replaced his take down pins in his MR556 and now he has the typical upper/lower loose play that IMO less quality AR's exhibit.
i hate A1 pins with tool for separate lower to upper
 
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The "tool" can be your standard .223/5.56 tip also for those worried bout losing it. As for me, I've changed my rear takedown pin to standard for ease of use/access to BCG but keeping the pivot pin as the detent one. Now theres only a miniscule amount of wobble between the upper/lower.
 

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The "tool" can be your standard .223/5.56 tip also for those worried bout losing it. As for me, I've changed my rear takedown pin to standard for ease of use/access to BCG but keeping the pivot pin as the detent one. Now theres only a miniscule amount of wobble between the upper/lower.
the pins of A1 are not made for have low wobble, only a remote reason not to lose, if you have pin holes and pins precise measures as there is no movement, if you have tried a few times and press the pins without original tool you can see, not always, the first piece you drop like other AR. Then I really do not understand the reason for which hk wanted to put these pins with detachable tool / bit the bullet, because I do not like
 

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Americanel i want to change those pin as well, can you please provide me the address where you have bought them?
Thanks
Feel free to PM me, or phone me or send me a text or facebook link

Ciao

CV
 

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I made the mistake of accidently slipping my tool and the detent flew out of the lower receiver. I spent the next hour and a half on my knees with a flash light looking for a very small black pin in my darkish carpet, my wife thought it was funny, I was pretty upset.



I went with YHM EZ Pull Takedown Pin Set and I have no receiver play, I am very pleased with these take down pins.

Thanks for this with picture did the same thing work perfect thanks for posting this.
 

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I ended up putting original pins back in I had the YHM EZ Pull Takedown Pin Set but the space between the upper and lower where really bad plus I had to fight get them in sometimes.
 
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