View Full Version : Modern Cotter Pin Firing Pin Retainer vs. Traditional Solid Pin
Hi Folks,
I normally don't even think of straying from mil-spec with any of the parts in my ARs (except for the LMT enhanced bolt, because, let's face it, it's made by LMT). However, I am the proud owner of a 1959-production Portuguese AR-10, and through my research contacts - I am the author of the recent Collector Grade Publications book on the AR-10 - I learned that the rifle I now own has a round count through it of roughly 40,000 rounds, many in full-auto mode, and never has had a part replaced (it cost me more than I are to admit to buy a spare extractor, extractor spring, gas rings, and charging handle as spares in case I need to replace parts in the future). This has given me a profound respect for the design of the parts on this rifle. This is what pushed me to make my carriers in all my AR-15s chrome-plated, and with the LMT Enhanced Bolt has relegated my previous BCG "A-Team" of Colt Carrier/firing pin/cam pin/retaining pin and ArmaLite Bolt to the backup role.
Aside from the chrome BCG, the other main difference in parts I saw on the Portuguese AR-10 that I actually could emulate in my AR-15s was the firing pin retainer. I am not overly displeased with the standard cotter pin type used today, although I have worn out and replaced 2 in the 25,000 rounds I have put through my modern AR-10. I did notice, however, that quite a few companies are offering this part in the original solid pin with split end, just like on the early AR-15s and my Portuguese AR-10. I know the ones from KNS have mixed reviews due to the split ends breaking from installation fit problems, but I have a source that makes stainless ones, and I am seriously considering giving those a try.
Does anyone have experience or engineering insight into these, and whether they might be more durable than the standard cotter pin? Also, is there any possible downside I am potentially overlooking, like them being too stiff or hard and putting too much pressure and wear on the firing pin or carrier, for example?
Thanks for your advice :)
The change was mostly driven by economics of manufacture. The current wire-style is easier and cheaper to produce correctly.
The old-style machined pin has to be turned, then have the end cut then spring tempered. During the early "testing" of the M16, such that it was, it was found that the drastic change in material thickness lead to the prongs being either too hard and brittle, or too soft and easily bent out of shape. The new-style, being wire and of a constant thickness are easily tempered.
There is no loading of this pin, so either is more than strong enough, if made right.
EzGoingKev
12-08-17, 16:39
KAC made their bolt with the solid insert. They put a roll pin in the bolt so the pin would not just pull out.
DPMS also uses the solid insert.
KAC made their bolt with the solid insert. They put a roll pin in the bolt so the pin would not just pull out.
DPMS also uses the solid insert.
Boy, now there is a night-and-day comparison of the best quality to the worst quality in the AR game. The solid pins I am considering are stainless ones that come from a well-known source I have used before who gets them from a military contractor. I am not sure I would trust the KNS ones, and DEFINITELY would not trust the DPMS ones. Hydrogen embrittlement is a problem with such parts, and apparently DPMS does not do the proper heat-treating to ameliorate the issue.
OP, I'm curious about the source of your SS FP retainer. You can PM if you prefer.
OP, I'm curious about the source of your SS FP retainer. You can PM if you prefer.
Oh do tell.
Please don't be like that, this industry isn't my bread and butter anymore, but I am curious about current events. Sometimes products are good/bad/indifferent that pass through some hands before public scrutiny. I would not want an open forum judgement that could lead to a company's future direction in this way.
At this time, X product is just that, not named.
Please don't be like that, this industry isn't my bread and butter anymore, but I am curious about current events. Sometimes products are good/bad/indifferent that pass through some hands before public scrutiny. I would not want an open forum judgement that could lead to a company's future direction in this way.
At this time, X product is just that, not named.
I didn’t mean it like that. I should have responded to the OP’s message, not yours. I was curious too and was hoping he would share it openly. My apologies.
Understood, no problem.
No worries 🤙
OP, I'm curious about the source of your SS FP retainer. You can PM if you prefer.
Sure thing, and no need to PM. It's from ar15sport.com. I know the owner, and a lot of the stuff he sources is from defense contractors. He has helped me get ahold of some really hard-to-find AR parts in the past, and always supplies good stuff. I don't get anything for plugging his stuff here, I've just been pleased with the parts I've gotten from him.
HK rifles use solid, captive pins.
I have used both. I find the cotter pin easier to remove during disassembly.
EzGoingKev
12-09-17, 12:41
There is no loading of this pin
That is not correct.
That is not correct.
How is it loaded?
militarymoron
12-09-17, 19:12
How is it loaded?
Every time the bolt carrier reaches its rearmost travel and changes direction the firing pin slams into the retaining pin.
Every time the bolt carrier reaches its rearmost travel and changes direction the firing pin slams into the retaining pin.
Which is the slightly less than the loading at the end of the recoil stroke (the buffer bumper takes a lot of the sudden stop out). The energy in the firing pin at the end of the recoil stroke puts a tiny dent in the brass primer.
If you take the bolt carrier group out of the rifle and shake it like a spray paint can, you have loaded the retaining pin about the same amount. That is not what is considered "loaded" in the engineering sense.
militarymoron
12-09-17, 21:02
That is not what is considered "loaded" in the engineering sense.
In the engineering sense, it's considered a 'live load' since it's moving; not a 'dead load'. It's still a repeated impact, however small.
In the engineering sense, it's considered a 'live load' since it's moving; not a 'dead load'. It's still a repeated impact, however small.
I will caveat the **** out of this as this might be over my head, and I've had more than a few drinks, but, if the cotter pin is steel, and a solid pin is steel, if both are getting a load that are below there respective break points, does it even it matter what type you use? If it does not, does it not make sense to then use whatever is cheaper?
militarymoron
12-09-17, 21:21
does it even it matter what type you use? If it does not, does it not make sense to then use whatever is cheaper?
Wouldn't matter to me; I agree. I'm not advocating using a solid pin; I was just pointing out that the pin does see a load, however small, during the firing cycle.
EzGoingKev
12-10-17, 00:29
If you have a bolt with an unshrouded firing pin the keeper sees a lot more than a small load.
StainlessSlide
12-18-17, 05:51
If you have a bolt with an unshrouded firing pin the keeper sees a lot more than a small load.
When, and in which direction?
When, and in which direction?I'd venture to take a guess that the load comes from the hammer (recocking it) when the carrier cycles back.
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EzGoingKev
12-18-17, 10:47
The firing pin comes in contact with the hammer during the bolts cycle. This contact pushes the firing pin against the keeper. It beats up the keeper.
My 6920 is an older model that had the half moon carrier with the unshrouded bolt carrier. After shooting a few thousand rounds through it I noticed the keeper was all beat up. I replaced it with a new one and after a few thousand rounds it was beat up too. I had never seen this on the M16 so I googled it and learned the cause.
The firing pin comes in contact with the hammer during the bolts cycle. This contact pushes the firing pin against the keeper. It beats up the keeper.
My 6920 is an older model that had the half moon carrier with the unshrouded bolt carrier. After shooting a few thousand rounds through it I noticed the keeper was all beat up. I replaced it with a new one and after a few thousand rounds it was beat up too. I had never seen this on the M16 so I googled it and learned the cause.Kinda offtopic, but what was the point in making a carrier with unshrouded firing pin?
I do understand the reason for a half-moon carrier (as idiotic it is...)
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EzGoingKev
12-18-17, 12:23
Kinda offtopic, but what was the point in making a carrier with unshrouded firing pin?
Colt did it so you could not convert the rifle to full auto. If the rifle was converted to full auto the firing pin would snap due to the high rate of contact.
Colt did it so you could not convert the rifle to full auto. If the rifle was converted to full auto the firing pin would snap due to the high rate of contact.OMG.. Just how stupid they were(are)?
Like half-moon bolt carriers and searblocks weren't enough stupid.
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Yep, and unlike sear blocks and half-moon carriers, the unshrouded firing pin was actually a serious problem, putting the stress of the hammer recocking on the firing pin and not the carrier. Thus led to the smaller-diameter "semi auto" firing pin, and the need to regularly replace firing pins. That was by far the worst way in which Colt butchered the AR-15 for the civilian market. As much as I love keeping things original, I will not fire an SP1 without first dropping a modern Colt or CMT M16 BCG in it.
EzGoingKev
12-18-17, 14:29
Yes, the firing pins took a beating too.
I replaced the parts in mine with an LMT FA enhanced carrier and a large shoulder firing pin.
Yes, the firing pins took a beating too.
I replaced the parts in mine with an LMT FA enhanced carrier and a large shoulder firing pin.
Duh, forgot that in addition to the Colt and CMT BCGs, I am a HUGE fan of the LMT Enhanced Bolt. I also am partial to ArmaLite's bolt, as it has the recessed 4th lug that balances the forces and causes the bolts to last a lot longer.
OMG.. Just how stupid they were(are)?
Like half-moon bolt carriers and searblocks weren't enough stupid.
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Gotta make sure the peasants don't get any funny ideas. Colt really goes out of their way to remind the unwashed masses that they are not the almighty government. Even when Colt is the only one supplying castrated parts anymore (which were never required and were solely of Colt's own initiative to begin with). And people talk shit about H&K...
Gotta make sure the peasants don't get any funny ideas. Colt really goes out of their way to remind the unwashed masses that they are not the almighty government. Even when Colt is the only one supplying castrated parts anymore (which were never required and were solely of Colt's own initiative to begin with). And people talk shit about H&K...
I must say I quite agree. I love the Colt parts in my ARs, but Colt is the spitting image of the FUDD company. They define those who are fine with the restriction or elimination of civilian rights to effective defensive arms, and only are about the bottom line with the government. Their stuff is excellent, but so are the mil-spec parts sold by a dozen-or-so vendors with their own label (only a few places actually make all the parts, including Colt's, which even used Anderson Manufacturing as their receiver OEM for a while). I consider Stag, which sells mil-spec CMT parts as the most underpriced sources of parts in the industry.
What a lot of people forget about H&K, is that they were ROYALLY screwed by the import bans of the late '80s and early '90s, before which they were offering lots of tactical rifle choices to the American public. Their knees were cut out from under them with the import bans and they lost a ton of money on their investments, so it was wise for them to be very skittish about getting back into the U.S. consumer market. Colt never had that excuse, as all their stuff was produced domestically and there was never a danger of an import ban for them, but they still gleefully supported and played into the gun ban agenda.
Of course, I still recognize that we suck and HK hates us, but my gripes with them are not that they are in bed with the fascist gun-grabbers, but that their stuff, while good and usually serviceable is so MASSIVELY overrated and overpriced as to defy comprehension. The G36 is just a barely-modified ArmaLite AR-18 made on better tooling with better materials. The G3 was a carbon copy of a VERY rudimentary Spanish battle rifle, for which the Spaniards (albeit with some freelance German engineers helping them) did essentially all the product development, and HK simply stamped their name on them. The CETME/G3 was so cheap and crudely made that the Spanish were offering them in competition to the FAL and AR-10 in the late '50s in weapons trials to prospective militaries for $45, while the FN FAL was going for $125 and the Dutch AR-10 for $110. All their handguns are less reliable versions of Glocks that are heavier, have lower magazine capacities, for which parts are much harder to find, and that are around double the price. The MP5 is simply a shrunk-down CETME that carries all of the crudeness and heavy weight of its big brother. Worst of all, however, is that blasted HK 416. Its mere existence is due to a bad batch of M4s from Colt that were giving the military troubles for a few months and were the reason behind the fluke of a reliability test where the 416 won. Every objective test done since has shown that the 416 is less reliable, has far shorter parts life, and fails at pitifully-low round counts next to even low-end ARs like PSAs in endurance testing. If you don't believe me, look up the disastrous experience Battlefield Las Vegas had with their 416s and MR556s. Even if the "increased reliablity" claims of the 416 had panned out, the system still is heavier, considerably less accurate, lacking in the ability to free-float a barrel, essentially impossible to effectively suppress, and utterly lacking in available spare parts.
Basically, I see everything HK has ever made as being like the Springfield XD; a basically serviceable but inferior product that, by some sublime mysticism or accident of history, is actually more sought-after and expensive than any of the weapons that considerably outclass it in every respect.
5.56 Bonded SP
12-18-17, 16:01
^ lol
I don't disagree with any of that, but I would love to hear the responses that would generate on a few other forums.
OMG.. Just how stupid they were(are)?
Like half-moon bolt carriers and searblocks weren't enough stupid.
Once upon a time, full auto carriers were considered machinegun parts by the BATF.
Colt is the spitting image of the FUDD company...they still gleefully supported and played into the gun ban agenda.
...The G3 was a carbon copy of a VERY rudimentary Spanish battle rifle, for which the Spaniards (albeit with some freelance German engineers helping them) did essentially all the product development, and HK simply stamped their name on them.
The reasons behind Colt changing the AR is much more involved than "gleefully supporting gun bans".
When Colt took steps to stop people from converting ARs to full auto, the political machine was pushing hard for strong gun control measures. The country was still reeling form the tragic shooting that took place in the Stockton schoolyard and the anti-gunners were rallied behind Sara Brady, Diane Feinstein, Nancy Pelosi and Maxine Waters who lead the charge to ban self loading rifles altogether. Part of the hue and cry was "It's too easy to convert these guns into machineguns". During that time, Colt was controlled by the company that owned Holley Carburetors who was strongly anti-gun. The boss of the Colt bosses.
Everybody was scrambling to slow the bleeding. The entire gun industry and the NRA were on the defensive. The Colt bosses were caught between their evil carbureted overlords and gun owners. To complicate matters further, many gun owners were willing to throw "assault weapons" to the wolves in hopes they'd leave us our hunting guns. In the middle of all this chaos, Colt made changes to its AR. It was said by our SMEs of the time (although we didn't call them Subject Matter Experts) that Colt made these changes hoping it would placate lawmakers enough to stave off more gun legislation. It didn't work. They passed the "assault weapon" ban in California which became the template for the following federal ban.
The HK roller block is actually pretty ingenious, even if it is very Teutonic in nature. In many ways, the system is very simple but at the same time, features rather sophisticated engineering. The HK91 did evolve from the CETME which HK licensed from CETME. Ludwig Vorgrimler developed the CETME for Spain based on the roller lock system of the StG 45 which Vorgrimler developed while working for Mauser. HK did more than just stamping their name on the CETME rifle. They licensed the design from CETME and refined it over time. It proved to be a rugged battlerifle.
This thread has gotten me gleeful.
Grinning ear to ear while at work being edumacated more on firearms and firearms development history.
Thanks to you all for the great civil rapport on this topic.
As the AWB was before my time, it's very interesting hearing about it. I certainly can say that I feel very VERY lucky to be part of the generation that came into legal gun ownership after 2004.
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