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



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...



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




I only tap about 1/8-inch or so... The detent doesn't even get close to the threads...

might not be a bad idea for the selector detent as well.

Originally Posted By 7point62: might not be a bad idea for the selector detent as well.

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.

I was just thinking as insurance if for some reason the grip broke off the selector will still work.

I think that I may just mod my SHTF gun, just cos.

That is a great idea!

Thanks!

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...<><....:)

I do this with all my lowers.  

bump

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

Great idea. I might try that on the selector spring.

Thanks.  Saved as .doc as usual.

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.

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

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

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.

You're smart.

Quarterbore,

Does the tap have to be 4-40 or could you get away with a 6-32?  

Thanks

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.

back up again

Very impressive.
TAG.

...

I found the set screws at Fastenal.....had to buy a pack of 100, so after a buddy and I did all ours I now have about 90 left. Anyone need some? lol

If you're giving them away I could use 3.

As someone that broke his new M&P15x (had to go to an armorer and get a new spring) putting on the Noveske QD End Plate by bending that spring I think it is a great idea.

btt

Now this is a great little bit of ingenuity. Thanks

Cool idea, I'll be trying it once I get home

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.

I picked up my 4/40 tap at Lowes. They had plenty. I also had to get  a box of 100 screws.

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.

You might use the idea on the selector spring, but not using 4-40 tap and set screw.  The hole is bigger.

Wow... great idea..... this should be the way every AR is made.... then we could argue over whether this change is needed or not...

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.

I have done 2 works great

Do you have to loctite the screw?  Does it come loose after firing some rounds are through it?

Think I might give this a go!

This is one of those, "Why didn't the original engineers figure this out and incorporate it into the design ideas!"
Great post!

did it to 2 of mine so far, i really love the idea.

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.

I doubt they knew how popular the AR would become with civilians and people like us that like to build our own rifles

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!

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.

Still a great thread after all this time!!!!

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.



 

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.



 

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.