I clicked on this thinking “how much could there be to it” but clicked all the same knowing Ian would blow my mind. As always, he did not disappoint. Thank you as always!

"How typically Swiss is it to manufacture a pin that is capable of malfunctioning" 🤣 I'm heading in to work this morning to address some Swiss metrology equipment that is overly complicated and is always breaking down.

I am an electromechanical engineer and this explanation is simply spectacular. A huge envy to Ian who can show so many examples with their own weapons. I also think I should send a shout out to Ryan (who asked the question) because it's one of those aspects that we don't usually consider but are very important when designing. Greetings from Patagonia Argentina

As an Austrian I have to disagree (slightly) on the pin on the AUG not being captive. In standard military use the pin is actually captive, as it contains the rear sling mount and you can not really remove the front sling mount. So the pin is not captive in body of the gun, but it is connected to the sling.

Mechanical Design Engineer here - in my experience most initial designs have all sorts of features to improve the quality of life for both Production staff and end users, most of which get cut once management decide they need to meet some ridiculous profit margin..

I love this new Q&A format!

In my experience the AR rear detent hole is a single diameter. The detent pin will happily come out of the hole into the take down hole. The pin itself keeps the assembly together.

This is a question I’ve wondered about for ages. Makes sense that it isn’t always viable. I think the H&K solution is the ideal middle ground if you can’t have captured pins. At least provide somewhere on the rifle to keep them secure and safe. Because if you drop a pin in tall grass it’s just gone. It’s honestly just such a different set of design criteria for a service rifle vs a commercial rifle, you have to grunt proof everything.

When a solder loses a pin, the captive pin is worth the trouble..Great video with perfect examples of the pro's and cons of captive pins..

The AR15/M16 rear take down pin detent hole is 0.094" and is not stepped as you said. I think you are confusing the selector detent hole which is internally stepped.

One trick for guns that do not have captive pins: Get a full replacement set and attach it to or find a way to install them into a cavity in the stock. If you have replacement parts on hand you will never need them. If you want a belt and suspenders approach, get two sets, one for the stock like I mentioned before and one for your cleaning kit.

Ian really deserves a lot of subs because he answers the question really well plus he explains them through giving us demonstration and setting up examples.

The AR15 style takedown pin is just way too complicated. The Swedish AK5 (FN FNC) has a captive takedown pin similar to the VHS-2. The pin is a single diameter with a ramped smaller diameter near each end. Around the pin and inside a milled slot in the receiver wall is a horseshoe shaped bent wire clamping around the pin, thus locking the pin in either the in or out position by springing into either smaller diameter end-groove. Being a mechanical engineer, this seems like a way cheaper and easier to manufacture solution than drilling tiny holes for coil springs and detent balls and milling keyways in the side of the pins. Also, both takedown pins are identical using this solution. You should take a look at it if you have a chance, Ian.

This brings me back to my high school engineering class I took. There are many factors involved even when wanting to use captive pins on a weapon. Materials, Cost, layout, and complexity all play factors into it.

Ian I just want to comment that I love this new Q&A format. I never really had a good reason for not watching the hour+ long Q&As, but these closely match your standard video format and I think that is what's working here.

In an AR, the wall thickness is wider than it needs to be to allow for the hole for the spring and detent. It could be thinner and lighter if it didn't have a captive pin. Same for the fire selector detent.

@Forgotten Weapons 3:58 A reminder from a retired Austrian Army NCO who used AUGs for over a decade (and still does in the army reserve): *_Never_* pull that rear pin out right away on a Steyr AUG. Instead, do it like you did it in your video about the AUG where you did it the right way: push in the indentation on the buttplate, *_push_* the pin *_in_* all the way, remove the buttplate, push the "button" thingy on the rear of the fire control group, *_and then_* pull the pin out. There are two reasons why you should always do it this way: 1) Disassembly is a lot easier and smoother that way, because the two C-shaped thingies on the buttplate aren't in the way when you pull out the pin, so it's much less fumbly to get the pin out; And second (which is more important): if you pull the pin out right away like you did here, the pin as well as the two C-shaped thingies on the buttplate can get worn out over time which - as you might imagine - ain't good. I've experienced two _really_ old AUGs during my stint in the Austrian Army where the buttplates didn't have a snug fit on the stock anymore because they were disassembled in that wrong way too often by careless handlers and thus needed new buttplates because the C-shaped thingies were just worn out too much. And while this might sound like me splitting hairs, it's actually just a) good form, and b) following the wise tried and tested principle of: "always take good care of your weapon, because then your weapon will take good care of you when you need it". Apart from that: still a great video, of course!

I love it when Ian nerds out on technical details.

That was a great breakdown, makes you think more about the engineering than just a feature list. Good stuff Ian.

I like what HK did on say, the G36 (or so I think, I don't have access to firearms in general): They have little holes in the stock to park pins in while you take the rest apart. Seems like a good idea for not losing pins in the field without making them captive.

So as a swiss I've only seen two material failures on the SIG 550. The rubber parts, the stock rubber part and the charging handle. I know people that haven't cleaned their rifles in years and never heard of captive pins that stuck.

A tiny remark on 8:20 - right above the hole I can see the circular witness mark from manufacturing, hinting that the hole might have been molded in - which would be somewhat superior to machining it.

A moment of silence for all the dropped pins out there. Lost, lonely, replaced and forgotten.

I've spent some time with SIG 550s, there are issues, but the pins malfunctioning, while it may happen, is not something that I remember happening to any of my soldiers or fellow NCOs.

i mean that swiss style of takedown pn has been used since the 60's so if it had problems they proberbly already fixed them

Some German Army instructors teach an advantage that non-captive pins have: you can install the pins from your non-shooting-hand-side, so while your rifle is slung and rides along your body, there is no way the pins get pushed out of position by equipment etc.

If your designing a rifle for a sport shooter to clean/dissemble at leisure captive pins aren’t essential. A combat rifle might need to be dismantled at haste and under pressure so captive pins make the process much smoother and reduce the risk of loosing parts.

I was in the Army during the time of ACUs and excessive velcro patches. In theory, us privates weren't supposed to disassemble the bolt of our M16s while out in the field because the firing pin retaining pin and extractor retaining pin are so small and easy to lose. I went ahead and disassembled everything anyways, but put those pins underneath my rank patch. Say what you will about the many many many flaws of that uniform, but it was nice to have a place to stash small gun parts.

Surprised you overlooked the captive wedge on the AUG that holds the receiver and the stock. Though it's not a pin as such, despite functioning as one.

Ian, I've been watching your videos for YEARS. I always walk away having learned something brand new. I love these short Q&A videos. Keep up the brilliant work!

Captive pins have an anecdotal risk of damage to the receiver while disassembled by people who don't know the risk of leaving a captive pin extended. That is to say I've heard of (mostly new owners) disassembling, leaving the pin extended, dropping the receiver, and the receiver falling on the pin in such a way that it breaks the receiver (from pin on stoner designs). Rather than risk learning this the hard way many simply push the pin in while the receiver is disassembled. Similar to not leaving a hand drill with a bit in it when not being used.

I like this new "discrete question" format for the Q&As. I never watched the long, omnibus ones, but here I'm alerted to the existence of a specific question that interests me and I can easily watch just that part.

I’m really enjoying this new format for the Q&A. I hope Ian continues this going forward.

@AUG: The rear takedown pin on an AUG might not be captive, but on a military rifle it is always fixed via sling to the receiver. And as such not prone to losing.

I am greatly enjoying this new Q&A format. By focusing on one question per video you provide such an in-depth and thoughtful answer. Loved the in-depth look at examples in this video to demonstrate your point.

If you're not doing captive, which as you've shown doesn't work with every material and design, I think the HK solution is probably the most soldier-proof because it has a defined order of steps. Yes, the take out and replace sort of thing Russell has pointed out with the KP15 works, especially since most folks will just remove one pin and shotgun the receiver open, I'm curious how many times it would take Private Schmuckatelli forcefully closing the upper on the pin accidentally to damage the pin, the rear pin hole, or the front pin hole. The average KP15 owner is probably a few rungs above guys who buy V6 Mustangs at criminal interest rates.

I love the long session Q&A which are almost like a nice me time podcast. I love this format even more. The fact that each question gets its own video makes it so much easier to reference.

I loved this and loved you showing us the different intricacies and work around solutions people made. Awesome

When talking about the ar15 the captive pins were an ask from the us army if I remember correctly. Your own collection will show that the original ar10 was designed with non captive pins.

The FNC design is quite simple and should work on polymer receivers as well. The (captive) pins are round and can rotate freely. They have two grooves around the circumference, to hold them closed and open. The captive mechanism is just a fairly thin wire locking pin installed in a slot in the receiver from the top. They can be removed with just about any pair of pliers. If they get bad, remove them, bend them to get a tighter grip and reinstall. Simple. The pins seem to be turned on a lathe anyway and the receiver is milled. So there probably weren’t many extra steps in production.

Thanks Ian! Great format and appreciate the attention to detail you bring to us. Always fun and informative.

There are other ways to retain pins too. In some cases a part that is installed more or less permanently could have a feature which the pin would stop against. This can all be molded into a platic assembly easily enough. Havent seen it on any guns but have used something like it for a different project. A pin type part bad to not rotate so we had a macined flat. Assembling two parts together trapped that pin part in the bore from either being able to fall out or rotate. One part had the bores and the other part had a flat which just protruded past the bore and mated to the flat on the axle. There were some tolerance issues at first but it was easy to sort out. I could see this on some guns such as having a little shelf on, say, a barrel trunnion or on a grip frame which is indexed perfectly to retain a cross pin. No tiny holes or extra parts to install, just a pin with a flat machined into it.

I have to say, Ask Ian is one of the cool things you did on your channel recently, I love it.

Really like this format for the Q&A Ian ! Great work as always. N

As someone who never watched the long QnAs, I’m enjoying these short QnA videos and learning in the process. Smart change Ian

I really like these question specific videos! It's much more easily accessible than the longer Q&A's (which are still awesome nonetheless).

I think it is more appropriate to say that the difference between the kp15 and the aluminum receiver is due to the manufacturing process rather than just the pure material properties. To add a retractable pin into the mold adds cost and complexity to the mold and the engineering involved. Whereas with the aluminum lower, if the blank in already positioned for machining of necessary features like the buffer tube thread then the cost of a small hole for a spring is tiny in comparison. Take a look at the front take down pin spring bore on the kp15. Notice that there is no bulge for the spring? they've changed the geometry of the receiver and removed the home for the pin all together because they are trying to maintain a uniform wall thickness (within reason). If they added the bulge and decided to machine it after it is risky and costly. It could require them to machine in an orientation that they wouldn't otherwise need which adds cost. It could also result in a void in the center of the bulge and prevent you from having a nice straight smooth bore.

Superior video. I feel kind of stupid because I didn't think about putting the pin back into its hole (even though I often screw fasteners back in their holes as not to lose or get them mixed up when working on other things). I love when a video teaches me something especially when it's something practical.

Something else to consider from the manufacturing cost side when making detents and captive pins: the tool to make the holes for the detent is almost always a custom tool. Machine tooling gets expensive fast and custom tooling like that even more so. Plus if you are a company that makes multiple parts on a single machine, getting the machine set back up and getting that detent operation correct takes some fiddling, assuming we're talking machined parts here.

I've thought of this every time I'm crawling on the floor with a flashlight looking for a dropped shotgun trigger group pin. Nice video, sir.

I'd also add another note to this video. Tooling. Most companies will be either buying their pins from someone else or manufacturing in house a commonly used pin en mass for many guns. Creating a relatively reliable, (no worse than a non-captive pin), self captive pin isn't that difficult. And the extra steps once your upto manufacturing sufficiently large numbers of them isn't a huge cost negetive either. But justifying the up front investment to do the new tooling setup is going to be hard without a serious need allready existing. And that largely isn't a thing ATM.

an entire vid about captive pins from Ian is like an entire vid about track tensioning from the chieftain. absolutely mandatory watch material.

Ian, I really like this shorter Q&A format. It's easier to pick & choose which question I'm interested in, rather than watching an hour long video with 6 different questions. Plus it's more bite-sized.

Great format for the Q&A's!

Three cheers! A great look at what appears on the surface to be utterly simple, but when examined carefully turns out to be very nuanced and situational. The new Q&A format is really going to be a great improvement. Thanks for the wonderful content, Ian! (edited for typo)

You should do more "disassembly table" Q&A. Not every question is suitable, but I really enjoyed the multiple comparison.

Well done, i really enjoy these sort of cerebral deep dives, more of this please!

I really like the format of these videos compared to the big Q&A. I know it takes more work, but I really appreciate it

Very well said, Ian. In 2018 I worked for a company making injection molded parts and as a mechanical engineer this was my first time dealing with them. Me, being a very traditional engineer, made my prototypes with fasteners. The principal level industrial engineer instructed me that while my design was stout and reliable, every single extra BOM item I add makes the overall product more expensive. If I could use say snaps that worked with the required draft for the mold pull, most of this consumer device would snap together once and never come apart. Where more precision was needed for a linear stage we used ground stainless steel rods but again, if we could reduce part cost by integrating the bearing into a molded part instead of trying to press or glue in a separate bearing it would keep costs down. While you obviously want the product, be it a consumer level device or even a firearm to be reliable above all else, if I can do that with 25% fewer parts it means that the client (even a military one) can get that many more firearms in the hands of soldiers. That was a side of engineering I was not exposed to, and you did an excellent job explaining it here. I also have to say for injection molded parts, thank God for CAD!

I always enjoy your videos Ian. It's very interesting to learn how guns work, and the different options such as open bolt & closed bolt systems. I live in the UK where mostly we aren't allowed to play with guns as a hobby, so the opportunities to handle guns and learn about how they work is very limited.

What a great question and as well a brilliant and detailed answer. I am really enjoying these more short-form Q&A videos from you Ian! I hope that these also appeal to whose who don't have the time to watch your spectacular monthly wrap-ups.

I'm surprised that there could be so much to this topic, but I'm not surprised that Ian knew and could tell us all about it.

No manager wants to wait for the engineer to get this amazing captive pin finished before making profit.

The Keltec RDB also has semi-captive pins although the furniture is mostly polymer. The pin hits a stop when you pull it out, but comes all the way out if you really YOINK on it.

That's the first time I've seen a captive pin on the VHS. My military issued rifle didn't have that. Not sure if that's an across the board product improvement or specifically done for the civilian market as I know the the guys in HS are well aware of the things americans love/fetishise over in terms of gun design.

An answer to a question I wasn't expecting to hear. Very well done Ian

Thank you Ian, been wondering about this myself for a really long time and you explained the reasoning behind it perfectly^^

Your knowledge and understanding of firearms is just amazing. Thank you, Ian!

Such a simple question, but an amazing answer. Loving this style of video.

This is outstanding stuff & so much better than hour long episodes. Excellent decision

So glad you made this video I’ve wondered the myself for quite a long time

Thanks for taking the time to show examples of captive pins. The VHS system seems to be the best idea for a polymer part because it spreads the stress across a larger area. Manufacturing the pin and retainer in-house may not be big deal for a large armes company. You should consider more videos like this that show how different gun makers solver the same problem!

There's another way to make the pin captive. And it's feasible both for sheet metal and polymer - axial profile cuts into the pin, similar to those on Steyr AUG rear pin, and a C-clip, traveling/tripping over them. Easy and cheap solution.

You do a nice job on these. I had several moments of "wait, but you can also do it like this..." and then you brought that up.

I wondered if this was also going to address captive recoil springs as well? They seem to have fewer downsides.

One method you missed for keeping pins captive was the sa80 solution of have a clip embedded in the steel body around the pin that stop it from being pulled out. Though these do come loose and need to be peened back into the slot.

HK do not have captive pins so they can ignore you when you need one. And after a LOT of efforts to get one, they can charge an arm and a leg to get a replacements.

Very nice answer, interesting indeed; glad we have engineers & testers to figure out what does & doesn't work.

The FN SCAR nailed it - just a little clip and a taper at the end of the pin. Just one extra part that’s incredibly cheap, and If it fails, no big deal, then it’s just a removable pin. The lower has a little pocket molded for it to hold it in place, but it is not load bearing, and still functions even if the pocket breaks. Such an elegant design :)

One of my favourite procrastinations is figuring out how would I design my own rifle. One of the things that I have been, "figuring out", are captive pins. Please feel free to make more of these types of videos :). Especially on the manufacturing side of weapons production.

Great analysis and commentary about design decisions.

Hello Iain another way of implementing a captive pin is used on the SA80 L85 (yes boo hiss lol) series of rifles. This is done on the steel sheet stamping where a boss is welded on with a groove inside. This allows a very thin diameter wire "C" clip made of spring steel to be inserted and that interfaces with the grooves in the pin and the boss. It does work and while not as strong as say an AR15 style pin it is pretty cheap and can be replaced with a little bit of fiddling.

you can also include metal parts in polymer injection molding (part gets placed in mould before plastic gets infected, can ve fully automatic process), for example a small diameter pipe for such a pin retainer. it does bring up the cost for the mould, of course, especially since you basically need three of them for every machine, but it's possible and wouldn't create a weak point like drilling into the part does. especially with an outside profile of the metal piece that'd help it remain in place and take over so evof the structure that's lost due to the void. the bigger problem with the last one is the abrupt thickening of the polymer as that increases the chances of imperfections or voids in the finished part, while the sharp corners do create potential for stress while cooling and therefor inherent weaknesses if not dealt with properly (which does increase cost once again, as there need to be special accomodations made for this).

I've seen captive pins in non-firearms applications in which they used a C-clip that slid along the pin and was stopped by a groove on the end of the pin. While not fool-proof, it does require deliberate effort to pull the pin through the clip and seems like a good solution for sheet metal components.

Great question when I heard it the first time. I was actually amazed that captive pins could be removed at first. Now I know that’s adding complexity to a simplified machine. Obviously the people who design guns use all the laws of physics and natural observations. The conservation of energy is amplified in this equation. But heat pressure and gravity are all about the biggest thing

Ian, I will point out on your comments from the MDR... Most plastics manufacturers will have those holes pre-planned in the mold. what they do is use insert pins while making the part to create these features instead of drilling holes. this eliminates the problem of having to weaken the polymer, but it adds more cost to your tools and dies for the part itself. P.S. - A lot of people are going to disagree with me, but you'd think the engineers at Desert Tech were not stupid, and more than likely did just as I said; used tool inserts while molding the part to create these captive pin features instead of drilling holes post mold-shot. it's common practice among a lot of polymer part manufacturers. P.S.S. - After some analysis of paused stills of the video, the tooling may have been simplified by using fixed extrusion pins machined into the mold tool, and although i can not see a parting line, the likely answer is that the die draw is going the direction of these features, which means that the mold opens and closes the same direction of these features, simplifying the tool and lowering the cost. At least that is what would have been done at the company i worked at as an engineer. Most of my work dealt in plastic parts manufacturing, as well as sheetmetal and welding assemblies. (Automotive supplier, in case people are wondering)

The SCAR has a captive pin on a polymer lower that is very sturdy and simple, a spring clip just pinches it in place, slotting into grooves machined in the the diameter of the pin.

Honestly, I’m surprised this question took so long to come up, given the always enthusiastic “this part is held together by this pin, which is captive which is always nice so you can’t lose it” uttered by Ian every time he comes across and shows us a captive pin. I was hesitant to ask this myself and sound like I was missing the point, or overthinking the pin. It’s a pin! I was satisfied with the “not all pins are captive, and not all pins are nice, but if a pin is captive it is always nice” proposition. I miss those simpler days.

I really like the short format single topic Q&A format

Additionally, to introducing a weak point in polymer parts there may be another issue that I think might be even more significant in some cases: A long hole for a detent and it's spring means a sudden decrease in material thickness over a large part of a certain cross-section. This can be a huge headache for injection molding processes, which are often used for polymer parts, if the axis of the hole is perpendicular to the direction of flow of the molten material. If there is some material added around the hole for strengthening that would even exacerbate the problem of rapid changes in material thickness! The issue is that the molten material flowing through the narrow section at the hole can cool down and solidify before enough material can flow though to areas “downstream” of the narrow section. This will sort of “choke” the flow of material and cause holes or shrinkage in the parts.

Man, what an excellent question. I had taken captive pins as a fancy and high cost benefit but never really considered why, or the possible downsides to them.

loving this series

From a machining standpoint, most of the non-captive pins I saw in the video could be produced on just a lathe. Even with the side hole for the ball bearing or the slit on the end for the HK style pins. With the AR style pins, the track or slot down the length of the pin would require a whole second setup in a mill. Even if it's just a simple slot, it's still going to add time, cost, and (minor) complexity to the supply side that may make it a nonviable option.

Neat content! I had never thought about captive pins before! Thanks!

Yes, I've always thought when learning about a firearm, and the pins are not captive, why? Now I know. Thanks Ian.

Great video. Wish you would have looked at the M&P 15-22 as well. Polymer with captive pins.

My tavor 7 has captive pins, guess I'll have to examine it closer to see what makes them captive. Thank you ian, you've enlightened us once again!

HK might not feature captive pins, but on the german standard issue G36 there are holes in the shoulder rest, specifically designed to take the pins during disassembly. I found that to be a very sensible and well thought through solution.

Good coverage of the question.

the Kel-Tec KSG has a sort of work around by having holes in the grip that allow you to easily store them. a cheap and simple solution to at least prevent them from rolling or needing a pouch