[ Why Don't More Rifles Have Captive Pins? ]
Hi guys, thanks for tuning in to another "Ask Ian" Q&A video on Forgotten Weapons.
I'm Ian, of course, and today our question comes from Ryan on Patreon.
And Ryan asks, "Why do more rifles not have captive takedown pins?
It seems that if someone is developing a rifle from the ground up
there's almost no drawback to captive pins,
especially if the rifle is going to be widely fielded. So is there some hidden cost?"
The answer is, I don't know that it's necessarily a hidden cost
but there is definitely a cost, especially an engineering cost, to having captive takedown pins.
And I think it is largely involved in the type of fabrication of the rest of the gun.
Because there are some situations where captive takedown pins
are actually not that difficult to integrate,
and there are some situations where they can be very difficult to integrate.
So let's go over to the disassembly table
and let's take a look at a couple of examples of rifles that do and don't have captive pins,
and see why they do or don't have them.
I think the best example people probably have of captive pins being a thing
and being helpful is the AR-15, so let's start there.
Just going to start with my rear captive pin here.
Now let's first consider what's required to prevent that pin coming out.
Well, there has to be some sort of detent to keep me from just pulling the pin all the way out.
And so if we look at the side of the pin here,
you can see that there's a little track milled in the pin.
And then we have this feature on the lower receiver itself.
That has a spring back here and a detent in the front.
And what's important to point out here is that in order for this to work
you have to have a way to install the detent,
and to prevent the detent from coming out the front of this hole.
So this is some of the engineering cost of having captive pins.
First off, we have to make arrangements to have a hole that we can access, in this case from the back.
So this is a two diameter hole.
It's going to be a larger diameter here until it gets up really close to the front,
and then it's going to get slightly narrower so that you can
put a little bit of a neck on your detent.
So you put the detent pin in the back and it can only protrude out a certain distance
so that it puts a reasonable, stable amount of tension on the pin itself.
... I don't know if I would call this a hidden cost,
but it is definitely an additional engineering cost to ... having a feature like captive pins.
Now this is still an AR-15, right? So it should be the same.
And yet the KP-15, the receiver for the What Would Stoner Do rifles,
this does not have captive pins.
... There's some difference in the architecture back here that could explain it.
But there's no difference up in the front, right? So why doesn't this have a captive pin?
Well the answer is we have a different material that we're working [with] here.
And in aluminium you can drill a little tiny hole
in the front of this aluminium feature and that's not a problem.
But polymer is not as strong, and if you drill a little tiny hole
into a thin piece of polymer you are very much creating a weak point.
And so rather than risk having breakage on the parts,
you will find (especially when manufacturers are working with polymer)
that it may not be feasible, just given the architecture of the part,
to have a hole for a ... spring and a detent pin to give you a captive pin.
And you'll see that in other polymer receivers as well.
So if we look at the Steyr AUG here,
we have a pin that's held in place by basically a part in the fire control group,
but the pin itself is not captive.
Why? Well, because you've got a polymer shell here.
... You could in fact drill a hole from the back
to put in a pin and a spring to retain the takedown pin,
and yet you would create a thin weak point in the receiver back here.
So again, no retention on that pin.
But what if we go look at HK?
Surely HK, it's a widely fielded military rifle, been used for many decades.
It's made out of metal, polymer shouldn't be an issue here, so why does HK not have captive pins?
Well this may be metal, but it's stamped sheet metal.
There is no space in this part to have a retention mechanism for that pin.
Now one thing you could do is the Swiss solution.
I apologise, I don't have a SIG 550 here to show you,
but we do have a little bit of video footage from disassembling one.
SIG opted to use pins that have their own built-in retention mechanism.
Which is cool and clever, but that's also just begging for something to go wrong with the pin.
A little bit of dirt, a little bit of rust, and pretty soon
you've got a pin that can be maybe solidly jammed in the rifle.
And now is the benefit of having a captive takedown pin
which is ... certainly not necessary, it's just convenient, is that worth the potential risk of,
"Now I can't disassemble this rifle because the pin has malfunctioned."
... How typically Swiss is it perhaps to design a pin that is capable of malfunctioning.
Say what you want about HK, but that pin really isn't going to malfunction.
So, what we fundamentally see here is that there are structural requirements in the parts
that have an impact on whether or not you can have captive pins.
Now that being said, let's take a look at a couple of cool examples of rifles
that do have captive pins despite having, say, polymer furniture on them.
A good example here would be the VHS-2, or as it's sold in the US, the Springfield Hellion.
This - like ho-ho!
Plastic furniture, plastic lower, plastic handguard, and yet that pin is captive.
So how did they do that?
Well, they have actually designed what is sort of a rivet-like part
that is screwed here, it's two parts screwed together into the plastic.
And this part itself retains the captive mechanism to hold the pin in place.
So this may not seem like a lot of cost, but it is a non-trivial cost.
So your pin is now proprietary.
This comprises two separate pieces that attach together,
and you've got I think three of them on the rifle total.
So you've got six more components going into the gun now.
And if you're trying to manufacture this in large numbers,
well now you've got like a couple of additional parts that
can act as a choke point to overall rifle production.
If you run short of these little doodles,
and your whole production line will shut down until you can get more of them.
So it's a cool solution here, I like it, but it's not something that is free of cost.
Just to play devil's advocate, here's an example of a design
that does have the problems that I elaborated earlier
and yet has captive pins anyway. So this is an MDRX.
And if I punch out this front pin, you'll see ... the pin's captive.
And it's got that AR style of groove milled into the pin.
And that means there's a spring and a detent in here.
Well, what they did was bulk up the polymer right where ... the pin goes through.
And then they just went ahead and drilled a hole in it anyway.
And they're accessing it through the pin, so if I push this in
you can see there's a little tiny hole drilled in the pin.
That will allow you to disassemble it by opening it to here,
putting a very small punch through to depress
the spring and detent behind, and then pull the pin out.
So they've gone ahead and done exactly what I said
wasn't a good idea on the What Would Stoner receiver, the KP-15 receivers.
... And they've just simply taken a different approach to what's viable.
They have been able to increase the amount of polymer here, but this is a weak point.
So perhaps this is a weak point in an area that's not getting a lot of force put on it,
that they don't think is prone to breakage.
And they're willing to accept having a couple of extra parts,
having to drill an extra hole in each of the pins, in order to give that functionality.
There you go Ryan, I hope that answered your question sufficiently.
I think captive pins are definitely a nice feature to have when they are feasible.
Of course if you don't have captive pins you can always take the pin out,
and then take the piece off and put the pin right back in it.
Or do the HK sort of thing, and have a specific pre-built hole in the stock to hold them I suppose,
if you don't want to put them back where they came from.
At any rate, as we can see, it's not always that super simple and feasible to add them into a design.
Anyway, if you would like to have your question answered in a format like this on video,
sign up on either Patreon or Utreon, that is where I take questions for these videos.
We have running threads each month on both platforms
for questions like this. Hopefully you enjoyed the video.
Thanks for watching.