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Simple fix for the rear takedown detent spring blues.... (Page 1 of 6)
Posted: 9/18/2008 10:51:37 PM EDT
[Last Edit: Quarterbore][Edited]
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Repost as the old one is in the archives...
archive.ar15.com/forums/topic.html?b=3&f=118&t=285950 In a thread in the EE I saw a number of people asking for the rear plate that retains the rear take down detent spring retained when using an AR-15 pistol buffer. To be honest, I got tired of fighting with that stupid little spring with my own AR-15 pistol years ago and I thought other people knew the simple trick to tap the rear takedown detent hole and then use a small allen head screw to retain the spring. Well, in case nobody has seen this done I decided to do this to a brand new lower I bought this weekend and my local fun show... First, the rear takedown detent hole in case someone is asking WTF is he talking about? 
A 4-40 tap with a little oil... Sure wish tapping an AK trunion was this easy as Alluminum is easy! When tapping the hole, if the tap gets snagged or stops turning, back it out, clean the area and try again. You should never have to force a tap and it should cut like butter when you are using some lube. 
Here is the tapped hole. Just blow it out with some compressed air when done tapping. 
You need to cut about 1/8-inch off the rear detent spring. If you don't do this when you tighten up the allen screw the spring will compress to the point that the detent will not come out of the divets in the rear takedown. (If you don't cut your spring, you will see what I mean ). 
1/8-inch 4-40 Allen head set screws. I got these at my local hardware for $0.10/each. 
0.5mm Alen wrench. Note a handy wrench like this makes it easier to keep the spring from flying! 
Set screw on the wrench. 
Place the shortened rear detent spring back into the hole. 
EDIT 1/12/2010 Comment Added from Page 4 of this thread by ARsRlikeLegos Use an thick grease compound or "swak" which is a teflon-style grease for SS/aluminum apllications when installing the set screw. Aluminum will gall (stick and the threads will come out with the screw) with most materials set screws are made of when installed dry. (Stainless steel is the most common due to its low carbon anti corrosive content) Some anit-seize compounds that contain copper or other fine metal powder can be too grainy and cause damage to the soft threads when taking the set screw in and out. I am sure most of you will not be taking the set screw in and out once it is installed, but Im just throwing my .02 cents.
Screw in the 4-40 Allen head set screw. 
The head of the allen head screw with a standard AR-15 buffer tube. 
So, what does this do for me? Now I can remove my A2 Stock and add a CAR stock with no wories of bending or losing that spring. With my AR-15 pistol, it makes it so that I don't need to use the rear cover plate. If I want to replace the spring for any reason, I just unscrew the set screw and cut off another spring and drop it in there... This is a 10-minute job and one I like to do on ARs that I swap stocks around on... Originally Posted By phillyd2: BTW, what is the purpose of that spring any way? The rear takedown detent spring is used to hold the detent against the rear takedown pin so it does not fall out of your lower! See www.quarterbore.com/library/pdf_files/tm9-1005-319-23.pdf PDF page 196 to 200 Originally Posted By engineer2001:
Is the spring strong enough to not bunch up and allow the detent to hang in the threads? In other words, could the spring get compressed when changing the selector and not uncompress because it or the detent was hung on the new threads? That and the chance I'd cut the spring too short is the only reason I can think of to not do this to my two lowers. I only tap about 1/8-inch or so... The detent doesn't even get close to the threads... |
www.Quarterbore.net
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Sure! I don't change my grips much so I don't do mine but it would be the same sized tap I am pretty sure. |
www.Quarterbore.net
My guns are not worth your life, but freedom and liberty are worth mine
My guns are not worth your life, but freedom and liberty are worth mine
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Great idea...but do you know how hard it was to find a 4-40 set screw? Nobody in 3 towns had them, I tried every hardware and auto parts store including ACE, Home Depot, Lowe's, and NAPA.
I finally found some stainless 4-40 set screws, but I had to buy a pack of 100. So, since I have extras, if anyone needs some, contact me. My email is through Yahoo. Bill. |
| I have been thinking about this for a while now and when I was at the hardware store on Friday I saw a 4/40 tap for $2.99 and picked it up. They did not have any 4/40x1/8" socket head screws at that hardware store but today on the way home from church I stopped at another hardware store that carries a larger selection of screws and bolts and they had 4/40x1/8" socket head screws, but only in SS, not in carbon steel. The SS version was $.35 apiece and I bought 3 to try. It worked slick and 3 of my AR's are now done. I will pick up a few more SS screws and complete them all....Merry CHRISTmas to all...<><....:) |
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I bought from this guy on calguns and had my envelope within 3 days. He sends a tap, the set screw and instructions. Easier than me going out and buying this stuff...
Click here |
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Originally Posted By Agro:
I bought from this guy on calguns and had my envelope within 3 days. He sends a tap, the set screw and instructions. Easier than me going out and buying this stuff... Click here I wonder if this guy has Quarterbore's permission to use his photos? |
| I don't care if they are used but it would have been nice to get credit for them. At least they are not uploaded to my server so he isn't using my bandwith to sell stuff too. |
www.Quarterbore.net
My guns are not worth your life, but freedom and liberty are worth mine
My guns are not worth your life, but freedom and liberty are worth mine
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Originally Posted By HoseKing:
Great idea. I might try that on the selector spring. I think you'd wind up with something like 1 coil on the spring since most of the safety detent spring is housed in the grip. This is such a great idea. I do it to all my lowers. Why the hell does QB keep having to repost it when it migrates to the archives? THIS OUGHT TO BE A STICKY |
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Originally Posted By Rich219:
Originally Posted By Agro:
I bought from this guy on calguns and had my envelope within 3 days. He sends a tap, the set screw and instructions. Easier than me going out and buying this stuff... Click here I wonder if this guy has Quarterbore's permission to use his photos? Just looked him up here on ARFCOM. Every post he has on here is selling this MOD or selling a LPK with the MOD http://www.ar15.com/forums/topic.html?b=7&f=125&t=648192 http://www.ar15.com/forums/topic.html?b=7&f=125&t=648189 |
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| There are two people selling a "kit" here on the site. They are making no more then say $4 per kit so I am hardly woried about that. One seller even links to this thread and I added a link here from the caliguns thread to make it clear. I don't care that people take the idea and put kits together as this was really shared to help others that are tired of fighting with those springs. |
www.Quarterbore.net
My guns are not worth your life, but freedom and liberty are worth mine
My guns are not worth your life, but freedom and liberty are worth mine
4-40 is the closest to the original hole size. To move up to the 6-32 I think you would need to drill the hole out. I get my 4-40 taps at sears but any reasonable hardware will have them or buy a kit off the EE 
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www.Quarterbore.net
My guns are not worth your life, but freedom and liberty are worth mine
My guns are not worth your life, but freedom and liberty are worth mine
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Originally Posted By Quarterbore:
4-40 is the closest to the original hole size. To move up to the 6-32 I think you would need to drill the hole out. I get my 4-40 taps at sears but any reasonable hardware will have them or buy a kit off the EE The 4-40 sounds like the right thing to do, considering the number of ARs that I need to get done. All the extra drilling is not worth the few dollars in savings. Need to go to the hardware store anyway for some rivets. |
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| This works well, the other thing you can do is get the KNS QD takedown pin and then you don't need the spring & detent anyway. |
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help me get this thing going- www.gunsonthestreets.com
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Originally Posted By Quarterbore:
I only tap about 1/8-inch or so... The detent doesn't even get close to the threads... I found that it is much easier to try the set screw in the hole to make sure the threads are deep enough before I start trying to push the spring in and then have to take it apart and tap a little deeper and start over. |
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I've done this mod on about a dozen lowers. Great mod.
At 1st, I was getting the set screws at a local industrial supply shop, but the shortest they carried was 1/2". I had to cut them down and then run then through the die to clean up the threads. I recently tried a local hobby shop. I was able to find a package of 4 shaft collars for about a buck and a half. Right size and didn't require any cutting. |
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Originally Posted By Raven1911:
Do you have to loctite the screw? Does it come loose after firing some rounds are through it? Not unless you aren't affixing a stock or endplate to it. The endplate/front end of the rifle stock fits right up against the rear of the receiver, so that should stop the set screw from backing out. There's another thread somewhere which discusses someone's 4-40 tap breaking off in the hole- I've done a few of these and never had this problem. It's not a bad idea to first practice tapping threads on holes drilled in a piece of aluminum bar stock (from a hardware store). Use oil on the tap threads (I put a drop of ATF on the tap threads, and it trickles down to where it's needed), twist the tap in slowly and carefully, backing it back out after every couple of turns and cleaning off the aluminum cuttings. You just need to tap threads down to ~3/16" depth for a 1/8" set screw. |
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Originally Posted By Milo5:
This is one of those, "Why didn't the original engineers figure this out and incorporate it into the design ideas!" Great post!  I doubt they knew how popular the AR would become with civilians and people like us that like to build our own rifles 
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I also don't think it was expected that some day people would be converting from pistol, to carbine, to rifle, and back
It may not be a perfect solution for everyone but for those that have fought with that spring the fix makes a lot of sense! |
www.Quarterbore.net
My guns are not worth your life, but freedom and liberty are worth mine
My guns are not worth your life, but freedom and liberty are worth mine
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Originally Posted By usmcgunman: Well I went out and got the tools but cant find the damm set serews! Guess this mod is on the back burner for a while. Some people use 4-40 socket set screws. 0.050" Allen key. Page 3-42 in the Fastenal catalog (new, volume #9) left hand column, first entry. I use 1/8" length 6-32 socket set screws. 1/16" Allen key. Page 3-42 2nd column, 2nd entry. Fastenal.com Grainger.com should have them as well. I didn't think of 4-40 screw thread, I have no input on better/worse. I'm a customer, no other affiliation. There are several kits here in EE that'll save you the trouble a diesel fuel going to fetch parts as well. Good luck whatever you decide. |
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Originally Posted By UNIT6639: Originally Posted By Milo5: This is one of those, "Why didn't the original engineers figure this out and incorporate it into the design ideas!" Great post! I doubt they knew how popular the AR would become with civilians and people like us that like to build our own rifles I thought that the field stripping/cleaning/service procedure was supposed to be do-able with a minimum of tools. Thats why comes apart with two pins, the tip of a 5.56 round and a screwdriver. |
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Fuck Obama
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Originally Posted By MetalGold: I just received my "kit" yesterday and in a matter of 5 minutes, modified 2 of my guns. The hardest part is gauging how much spring to cut for that perfect detent/pin slippie-slidie-feel. It's the same with cutting 1.75 coils off one gun safety detent spring, and 1/2 coil off another safety detent spring so the safety glides smoothly. |
Go Get Bo Bergdahl Back!
Fuck Obama
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Originally Posted By kaos:
Originally Posted By MetalGold:
I just received my "kit" yesterday and in a matter of 5 minutes, modified 2 of my guns. The hardest part is gauging how much spring to cut for that perfect detent/pin slippie-slidie-feel. It's the same with cutting 1.75 coils off one gun safety detent spring, and 1/2 coil off another safety detent spring so the safety glides smoothly. I just cut a piece off the same size as the screw and use the screw to adjust tension to a point that I like. |
Simple fix for the rear takedown detent spring blues.... (Page 1 of 6)
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