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Gunsmithing AR detent spring modification

SigTauJohn

Sergeant
Full Member
Minuteman
Dec 5, 2011
149
0
37
KC, MO
Saw this in a new magazine called "Recoil" and thought it was a great idea. Basically captures the spring in the receiver so if you swap stocks on your AR you dont have to worry about the detent spring flying out.


What you are going to need: 4-40 NC tap, 4-40 x 1/8" set screw, allen wrench (if your set screw is allen head), cap full of fresh motor oil or tapping fluid, tap wrench or something to use as one, 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!

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Also if you have a pistol configuration AR you wont need the plate between the reciever and tube now if you dont want it.

Enjoy! only took me about 10 min from tools out to put up.
 
Re: AR detent spring modification

Now that is a handy mod if you have a lower you are constantly trying new parts on.
I will definitely bookmark this one.
 
Re: AR detent spring modification

Damn good idea. I don't know how many times Ive chased a spring accross the room. Will add this to the weekend project to do list.
 
Re: AR detent spring modification

Sometimes you have to wonder why they weren't designed that way to begin with or even worse why subsequent designs never adopted it.
Good Work!
 
Re: AR detent spring modification

Some receivers come with this mod. I've done quite a few myself.
 
Re: AR detent spring modification

Just got 4 new springs cuz they fly at 188 FPS when you take the stock off and i can't find them. Thanks for the idea.
 
Re: AR detent spring modification

i do that to all my lowers. if someone needs one of those set screws, you can go to home depot.

there's also a mod for the Safety detent, that uses a ball bearing. i haven't tried that yet, but i've been meaning to experiment.
 
Re: AR detent spring modification

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: hdbiker1</div><div class="ubbcode-body">Some receivers come with this mod. I've done quite a few myself. </div></div>
Which recievers come with this mod...TIA
 
Re: AR detent spring modification

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ackleyfan</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: hdbiker1</div><div class="ubbcode-body">Some receivers come with this mod. I've done quite a few myself. </div></div>
Which recievers come with this mod...TIA </div></div>

Seekins does it on their lowers.
 
Re: AR detent spring modification

if you end up with some surface damage around the hole you can use Aluminum black to patch it up.
 
Re: AR detent spring modification

I do that to all my lowers, It also, will make the take down pin adjustable a little at least. So it is not so crazy hard to push out with your fingers. I have also done the same thing to one for the safety detent and spring. works well as well. Never worry about this stupid little springs and detents shooting out and getting lost in the carpet.
 
Re: AR detent spring modification

It's a nifty little trick, I saw that posted on another forum about 3 years ago when I assembled my first lower.
I've since done it with them all. Seems like a no-brainer.
 
Re: AR detent spring modification

Not unneeded but do this one as well if you dont want to pay 2 or 3 hundred dollars a piece for triggers on,,,,,well I have like 20 different ar15s now so this is great for me.

50 Cent trigger job
 
Re: AR detent spring modification

thats pretty cool. have you done that yourself? Is it worth the time? I dont run cheap triggers anymore but its not a highend trigger either...
 
Re: AR detent spring modification

I seem to remember someone throwing together a kit that had the parts to do this & it wasn't too expensive. I think I read about it on arf.com or possibly calguns.net. If I find it again, I'll post a link
 
Re: AR detent spring modification

couldnt be too much... $5 for a tap and $.19 for the screw...