AR Mod - Takedown Pin Detent Spring Retainer

[twarr1]

I just made this modification to one of my AR-style rifles. I'm wonderig why I never heard about this before? I've lost countless detent springs over the years.

https://twarr1.blogspot.com/2021/04/best-ar-mod-since-stoner.html

Basically, just tap the detent hole in the lower receiver for a 4-40 set screw to retain the spring.
... I wonder what else I'm missing?

 

[Pahonix]

That's a brilliant idea. I think this might be my weekend project!

 

[a5werkes]

I do it to all of mine. It was discussed in Recoil a few years ago.
Also replace the bolt catch roll pin with a hex head bolt.

 

[herrwalther]

Also replace the bolt catch roll pin with a hex head bolt.

Aero makes that standard in their M4E1 lowers. I never really had a problem installing the bolt catch pin once I got the right tools and blocks.
https://www.aeroprecisionusa.com/m4e1-stripped-lower-receiver-anodized-black

 

[a5werkes]

^^^ a number of mfg.'s are doing both as standard. Two simple projects just for fun.

 

[Blue68f100]

All of my Billet upper came that way. Nothing new to the higher in parts.

 

[Blkhrt13]

I just made this modification to one of my AR-style rifles. I'm wonderig why I never heard about this before? I've lost countless detent springs over the years.

https://twarr1.blogspot.com/2021/04/best-ar-mod-since-stoner.html

Basically, just tap the detent hole in the lower receiver for a 4-40 set screw to retain the spring.
... I wonder what else I'm missing?

That’s a great idea thank you. I will definitely have a go at that. I may have some 4-40 around here somewhere already.

 

[redcon1]

I just made this modification to one of my AR-style rifles. I'm wonderig why I never heard about this before? I've lost countless detent springs over the years.

https://twarr1.blogspot.com/2021/04/best-ar-mod-since-stoner.html

Basically, just tap the detent hole in the lower receiver for a 4-40 set screw to retain the spring.
... I wonder what else I'm missing?

I used a pair of hemostats to lock onto the detent and had the pin installed in about 30 seconds after about 30 minutes of fumbling with it with my fingers. Tapping the hole is an interesting idea though. I like it.

 

[Blkhrt13]

I do it to all of mine. It was discussed in Recoil a few years ago.
Also replace the bolt catch roll pin with a hex head bolt.

View attachment 994080 View attachment 994081 View attachment 994082 View attachment 994083 View attachment 994084 View attachment 994085 View attachment 994086 View attachment 994087 View attachment 994088

So are you drilling one side for clearance and tapping the other ?

 

[a5werkes]

Do not need to clearance drill anything, if you did you would have no material to use the 4-40 tap for thread making.
As shown, just 4-40 tap the hole for the set screw, insert spring minus 2 coils, insert set screw, no loctite necessary as the receiver extension
prevents the set screw from backing out. Although I couldn't help myself by a drop of blue loctite to the screw.

 

[Blkhrt13]

Do not need to clearance drill anything, if you did you would have no material to use the 4-40 tap for thread making.
As shown, just 4-40 tap the hole for the set screw, insert spring minus 2 coils, insert set screw, no loctite necessary as the receiver extension
prevents the set screw from backing out. Although I couldn't help myself by a drop of blue loctite to the screw.

I was referring to the other mod. Bolt catch screw pin.

 

[a5werkes]

The smooth axle on the bolt catch screw is the same diameter as standard retaining pin, so only the rear pin boss has to drilled & tapped. There is not much space between the front - rear supports so drill slowly and watch the drill bit tip until it is in the gap, stop. Drilling into the forward limb
even a little bit may alter the bolt catch screw axle fitment stability; same with the tap, use a bottoming style as a tapering or plug tap will be engaging the forward hole by the time the rear support is threaded. Quite easy modification, just needs to done slowly with correct tools.

 

[Blkhrt13]

The smooth axle on the bolt catch screw is the same diameter as standard retaining pin, so only the rear pin boss has to drilled & tapped. There is not much space between the front - rear supports so drill slowly and watch the drill bit tip until it is in the gap, stop. Drilling into the forward limb
even a little bit may alter the bolt catch screw axle fitment stability; same with the tap, use a bottoming style as a tapering or plug tap will be engaging the forward hole by the time the rear support is threaded. Quite easy modification, just needs to done slowly with correct tools.

I love the idea of this mod. I may yet wind up ordering the stuff to do it to mine. But other than deduced risk of beating up the lower is there a reason to need that pin out often?

 

[BreechFace]

This is why I buy Aero M4E1 receivers.

But I do have few other receivers that I haven't got around to doing this to.

 

[a5werkes]

But other than deduced risk of beating up the lower is there a reason to need that pin out often?

No. But when you need to, you will be grinning rather than cursing the standard roll pin.

 

[BBBBill]

The smooth axle on the bolt catch screw is the same diameter as standard retaining pin, so only the rear pin boss has to drilled & tapped...

Most of the time. I've found a few Anderson lowers where that does not hold true. Moral of the story is measure, measure, measure. Invest in a few gauge pins to check hole sizes and aircraft length drills of the appropriate diameter.

 

[BigBlue 94]

For the rear detent spring i use a 6-32 tap and set screw that is 3/16" long. Tap goes right in the hole, no drilling required. I drop the detent and spring in then cut the spring flush with the receiver. Then screw in the set screw.