Pictures are now at the bottom but they are blurry due to low light and crappy camera phone, sorry!!!

So I was reassembling my AR-15 the other day and I was messing around getting the take down detent spring back into place under the stock, and I thought "Why didn't they make these captured springs?" So I put myself to work figuring out how to do it, I did some measuring and it is about a 3/32" hole, so I would need a 4-40 NC tap to tap the hole and put in a set screw.

I called all around the city and -no one- had a 4-40 x 1/8" set screw, EXCEPT one place, which was closing 15 minutes after I called them. So no dice on the screw today, but I do have the tap, so I threaded it this evening.

If you want to do it as well, here is how:

What you are going to need: 4-40 NC tap, 4-40 x 1/8" set screw, screw driver, allen wrench (if your set screw is allen head), cap full of fresh motor oil or tapping fluid, pliers and crescent wrench to turn tap, paper towels....

1. Make sure rifle is unloaded. Pull the pins and seperate the upper and lower. Set the upper aside.

2. Remove: the stock, buffer tube, buffer detent and spring (set aside, make sure it doesn't shoot across the room when you take out the buffer tube), take down pin spring, detent and pin. Set all of this aside in order, don't lose the small bits.

3. Clean the area free of any debris, I personally used some CLP to spray out the detent hole to clean out any gunk in it.

4. Hold the lower firmly (or better yet clamp it down or in a vice with rags to keep from marring the finish) and dip the tap in the oil, then drip some of the oil into the hole. You want to make sure it is well lubricated.

5. Insert the tap into the hole and MAKE SURE it is STRAIGHT. We are dealing with aluminum which is much less forgiving than steel. Turn it by hand until it catches and you can no longer turn it. I then used a pliers to grip it by the end and turn (its easier to keep it straight than with a wrench). it should start screwing in, and you may see shavings start to come out. After you go a maybe 5 or 6 turns, back out the tap and clean the area out and relubricate. Keep doing this until the tap goes to the desired depth for your set screw. (It ended up being about half the length of the tap for me, it is tapered so its not cutting threads the whole way).

6. After you back the tap out the last time, clean out the area with some CLP and then maybe some compressed air, make sure all the aluminum bits are out.

7. Start to reassemble, put in the take down pin and then detent, spring. Then carefully press in the spring and start the set screw into the threads, tighten it till it is flush with the receiver.

8. Reassemble the rifle! Hooray!


Pics:

The lower with everything stripped away to get to the hole to be tapped:





This is the tap that we are using, its pretty tiny, around 3/32" (0.089 or so)




This is with the tap all the way in as far as I am going with it:





The shiny part is the end result with threads in the hole! Wooo

Bravo!  No more springs launching across the room into some nook and cranny never to be seen again.  

You forgot to include "cut 1/8th inch off the spring to allow for the hole now being more shallow due to the set screw insert."

No, your not the first to come up with this idea, btw.  Good idea, just been done.

Now you can come over and do it to my AR's friend of friends! lol.

In all serious excellent and very inventive solution to a bothersome task. Kudos!!

Haha dont worry KOTOC I will come over sometime and do the same mod if you want, just gotta find more set screws!

I've done this to a couple of my lowers. First time I tried it I broke the tap off in the receiver... oops

I started drilling it out, hoping to remove it. It got difficult to drill and I didn't want to ruin my lower... so I left the tap stuck in there, put the spring in from the other side and put it back together. MISSION ACCOMPLISHED.

The next time I was more careful.

You broke a tool steel tap off in an aluminum receiver?

Dare I ask?

Must have been a pain in the ass to get that spring, detent, and takedown pin all
in there and assembled like that.

Ok, I guess Im missing something.... does this spring have a function?  If you are effectively sealing it off with the plug, why not just remove the spring altogether?

it keeps pressure on the detent so the takedown pin isnt loose. you need the spring

After seeing this posted the 1st time, I retro-fitted the ARs I had at the time and I do this on every new lower I build.  It's a great tip.

I was buying the set screws at a local industrial supply place.  The only place at the time that I could find that carried the 4-40 set screw.  The shortest size they carried was 1/2".  I had to cut them down, then run them through a die to clean up the threads.  The local hardware and automotive places don't carry them this small.

I had an idea awhile back and followed up on it.  The local hobby store, they deal very heavily in R/C stuff, carried a collar kit with 5 collars for about a buck and a half.  The collar uses a 4-40 x 1/8" set screw.  This is cheaper for the same number of too long set screws from the industrial supply place.

I guess some of the lower manufactorurs have started doing this.

The spring has a detent on the other end of it that holds the rear takedown pin (connecting the upper & lower receivers) in.  You might also be able to do this with the spring behing the safety/selector detent.

FWIW; AFAIK; IMHO; YMMV; yadda, yadda, yadda.

Regards, Ed Mann
   [email protected]

Bobby Bowden is doing a fine  job - just leave him  alone.

I wouldn't on the selector detent spring.  You'd heve to cut too much off and it most likely wouldn't work right.  That said if you got a shorter / stiffer spring then maybe...

Part way in, it looked like it wasn't straight. I put a little sideways pressure on it and SNAP!



It was easy: I grew 3 additional fingers to hold everything in place.

Yeah it was tricky.

Nice. I was thinking about searching for this thread the other day so I could do this to my new lowers.

Just buy a Tactical Innovations or Sun Devil lower receiver. They come with the captured spring etc. right from the factory......no extra charge.


Thanks for taking the time do the description and the photos. That is an option if you don't have one of the above brands.

P7-PSP - thanks.. I had heard some manufacturers had started doing it I wasnt sure who all did it.

I am buying the tap and set screws tomorrow.

Why?  just get a couple spare springs in case you lose them.  Its a lot better than risking the breakage of a tap in your receiver.  If you have never tapped anything before, then you probably have no idea what I am talking about, or why I am suggesting caution.  Good luck.  But this is a worthless modification given the negligent cost of having a few spare springs around.





Installing and removing the spring is not hard.





 

so i only looked at the pictures ITT, and read the part about cutting some of the spring off.

2 question:

what is the TS trying to explain AND who cares if the detent gets stuck?  what am i missing?

i have a pistol lower with a 22 upper.  i cant have a stock and dont need a buffer tube.  with this mod, and a threaded plug, i can have a clean looking back end of my lower, without holding the spring in with my thumb.  

I did this last year....thought I came up with something new.

The likelihood of breaking off a tool-steel tap in the aluminum lower is very low.  It's dead simple and easy to do-as long as you use a little oil on the tap, of course.  I was a little surprised at how very easy it was to tap the hole; I had more difficulty cutting the spring for length.  As for the worth of the mod, it does remove a couple of steps from the process of changing out receiver extension tubes and/or stocks, and time saved is time saved.

Agreed. Unless you are turning the tap like a sombitch or you bottom it out, the chances of breaking the tap off aren't that great. Granted, it's still possible though if you're not careful and take your time.



 

Never cut threads on a firearm, but cut threads in aluminum and steel for other applications; as well as using oil, I found if you back out the tap and clean out the cut material before it builds up you significantly reduce the chances of breaking the tap. Seen recommendations to back out a bit every 3/4 turn, back out when you encounter an increase in resistance, etc.  The only time I've broken a tap is when I rushed it and was NOT careful to keep the cutting debris from getting wedged between the cutting tool and bore.  You can snap the tap if put a lot force on it in a direction its NOT intended to go as well, easier to do if you encounter greater resistance that requires more force, like cutting steel or cutting deep into a bore as well as NOT cleaning out the debris that is jamming it up.

I did a couple of my lowers, quick easy mod, and I found the 4-40 set screw at my local hardware sotre for something like 12 cents, bought a whole bunch because I have big ole bear paws that tend to lose little pieces.

regarding cutting 1/8" off of the detent spring, I would first try it w/out cutting any off, and if it's too tight, take a coil or two off at a time until it feels right.  I just installed the rear pin, spring and detent on my Dennys lower that comes with the capture screw, and it almost fit without cutting anything off the spring.  If you just start by cutting 1/8" off, you may find it's too loose and then need a new spring.

I'm just happy I'm not the only guy who loses those when they fly across the room. Same with the front take down pin spring...

but great idea man, I wonder if that's what spikes does? Hrm I never really checked that close.

In regards to the Safety Selector Detent, I recently modded mine by using a 1/8" ball bearing, 1/2" of the spring, and a 8-32 x 3/16 set screw. Works like a champ and actually switches with much less resistance and smoother feel to it. Quieter too I might add.

ACE hardware. somewhere between 10- 15 cents apiece.

Not having to fool around with keeping track of parts that do not need to come off the lower unless they need to be replaced is worth doing the modification.  When the buttstock is removed the spring, detent and takedown pin end up flopping around all over the place.  When you do this modification they stay put.  Cost of the modification is minimal, the cost of ordering spare springs and detents in minimal...  The shipping on the spare parts is ridiculous from most companies.

Been there, done that...

Cool.

holy resurrected thread batman....

How often are you switching the buffer tube/A2 stock? I must be doing something wrong.

While I tend to agree that installing and removing the spring isn't really that hard to begin with ... OTOH, I certainly wouldn't call the modification "worthless" either.

Matter of fact, IMO it looks like a great idea and makes me wonder why stripped lowers & LPKs don't come this way as standard for assembly.  

That said though, since I don't have a lot of experience with drilling/tapping/cutting this type of material, it's probably not something that *I'd* want to "experiment" with on one of my lowers.  

But, if I knew someone who had the tools and I trusted their skills, I'd most likely have them do the mod for me.

I've done upwards of a dozen lowers so far this way with no negative repercussions.
The tap literally turns in by hand and then I use a wrench to slowly and gently turn the tap in to make about 6 or 8 threads, and I clean it out halfway through....

Don't forget some oil - it helps collect the "chips" and smooths the tapping process a lot.

Honestly this is the easiest and smoothest "customization" I think it is possible to do with an AR.

Worth a bump.

If there is a concern about cutting a spring too much, the set screw could be turned in further if the threads allow it, adjusting the spring pressure.

The safety detent mod especially - getting it just right.

A related thread had a poster saying Spike's lowers now have this modification.