AR-10 high-pressure firing pin

[tangolima]

It is for stout rounds such as 7mm SAUM. But what makes a firing pin high-pressure? What would happen if a regular FP is used instead.

-TL

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[stagpanther]

I have a few installed in some older AR 10 builds--they used to sell them individually for all bolts but now seem to say they are only configured for their bolts. IIRC, the reasoning behind these pins may seem a bit counterintuitive; in some AR 10s users may have light strikes which may fail to touch off the primers so might be inclined to use a heavier/thicker firing pin--but JP found the opposite is true, the smaller, lighter pin has the better energy. Sorta the same reasoning behind using a heavier hammer is not going to make a better strike in an AR trigger group. In your case I'm not sure JP has a magnum bolt to go with their pin--but you can ask. They have been in the precision AR game for a long time so it's worth getting in touch with them.

[tangolima]

That's it? A smaller tip? Is it the same as enhanced firing pins some brands are selling?

This is dumb. A smaller tip in the same firing pin hole makes the tip undersized. It leads to premature primer cratering or even pierced primer. No wonder there are lot of that in the brass I have picked up from the range. I have been thinking they must be hot loads.

Failed to ignite eh. I bet it has something to do with weaker hammer spring people have installed to make better trigger pull.

Thanks for the info!

-TL

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[HiBC]

I know nothing about this product. This is the first I have heard about it.

Maybe it is about the new military 277 round.

What I have to offer is that we might want to be careful with the "AR-10" designation regarding firing pins. Only Armalite is an AR-10.
A DPMS, for example, is an LR of some designation.

It matters because Armalite designed the AR-10 firing pin with a spring around it to resist forward inertia ...Like the 1911 pistol has.

The 5.56 AR-15 has no such spring.

And ,for example, a DPMS LR 308 has no provision for such a spring.

Correct me if I am wrong, but an Armalite Ar-10 firing pin is not interchangeable with the generic .308 size AR clone firing pin to the best of my knowledge.

[tangolima]

It is dpms LR 308. No spring.

-TL

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[44 AMP]

But what makes a firing pin high-pressure?

Marketing /advertising

[tangolima]

Originally Posted by 44 AMP

Marketing /advertising

I was suspecting that. I bought a complete upper. It came with bcg with "enhanced firing pin". Small tip. Cratered primers happened midway to max load. I have been searching for firing pin with thicker tip since, but mostly to no avail. I bought a bolt with tighter firing pin hole from a buddy and that solved the problem.

I got lucky yesterday. Friend told me about Fulton's FP with 0.078" tip. It is the thickest I have heard. Cheap. Will order a few.

-TL



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[stagpanther]

I was suspecting that. I bought a complete upper. It came with bcg with "enhanced firing pin". Small tip. Cratered primers happened midway to max load. I have been searching for firing pin with thicker tip since, but mostly to no avail. I bought a bolt with tighter firing pin hole from a buddy and that solved the problem.

I got lucky yesterday. Friend told me about Fulton's FP with 0.078" tip. It is the thickest I have heard. Cheap. Will order a few.

-TL

In other words--if it ain't broke fix it? It might be worth considering the manufacturer has some experience with these things.

JP has been making these things for a long time. They know what they are doing. They make the point--and it's true IMO--that most people couldn't tell the difference between a system that is under-gassed and one that is over-gassed as the symptoms can be almost identical.

Since the grand inquisitor of the Armalite inquisition is back in our presence--I will refer to the larger AR platform as 308 xxx (don't want to upset the DPMS crowd, either).

[tangolima]

In my case at least, it is broken. I can see the point of smaller tip to promote better ignition (think Glock firing pin), but the firing pin hole should also be tightened. That's just gunsmithing 101. Maybe that's why some of them have stopped selling the individual pin?

Anyway I have just ordered 2 0.078" pins from Fulton armory. Hopefully that will end my quest.

I'm still contemplating 7mm SAUM project. Just miss x-caliber sales. I will wait. This new pin will be fitted to the magnum bolt.

The bolt with small firing pin hole that I bought from my buddy, it happens to be JP.

-TL

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[HiBC]

Since the grand inquisitor of the Armalite inquisition is back in our presence--I will refer to the larger AR platform as 308 xxx (don't want to upset the DPMS crowd, either).

I'm not upset and the attitude is uncalled for. The Armalite AR-10 has a physically different bolt and firing pin. The parts are not interchangeable.

I'm not nit picking terminology.

Maybe you are unaware of the difference. I have worked with both guns.
Stick around,you'll learn.

[44 AMP]

The function of a firing pin is to detonate the primer by transmission of spring force.

In this case, spring drives the hammer, hammer hits the firing pin, firing pin hits the primer.

I don't see anywhere in that where the use of the term "high pressure" is correct or appropriate.

The force of impact of the pin depends on the mass of the pin, and its speed. Surface area and shape of the tip play a part in ignition, and the relationship between the size of the pin and the firing pin hole (and channel through the bolt) play a part, before and after ignition.

When one outfit makes the bolt, and another makes the pin, tolerance and fit issues can happen, even in "standardized" designs.

And when you add in different parts makers selling their idea of "improvements" things go off the map, quickly. Uncharted bogs and pitfalls abound, along with the occasional sleeping dragon.

[tangolima]

I think dpms has somehow become the main stream. I just use the terms interchangeably but I always mean dpms.

I am sure panther was joking, even though there weren't any emojis in his post to convey the humor. Humor may not be much humorous if it requires illustration.

I thank you all for the information. Much appreciated. (No humor)

-TL

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[stagpanther]

High pressure means exactly that--and it has a specific meaning and impacts how biglee 10's and smallee 15's operate.

I'm not upset and the attitude is uncalled for. The Armalite AR-10 has a physically different bolt and firing pin. The parts are not interchangeable.

I'm not nit picking terminology.

He didn't say he had an Armalite--did he? And yes, you are nitpicking.

[tangolima]

Firing pin exerts force over smaller area (smaller tip) and hence higher pressure on the primer. I thought the FP has special feature that better handles the higher chamber pressure of magnum cartridge. It doesn't really.

-TL

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[HiBC]

He didn't say he had an Armalite--did he? And yes, you are nitpicking.

He said he had an AR-10. Only Armalite makes an AR-10. If that means something different to you, the problem is in your thinking.

The DPMS is built like the AR-15 . Pull the retaining pin out of the bolt and drop the firing pin out.

The AR-10 ,pull the retaining pin,drop the firing pin out,but looky there! A firing pin rebound spring comes out! A whole 'nuther part!
I'd guess its there to lessen the firing pin impact on primers when the bolt slams shut.
And,to make up for the spring length,the shoulder positions are machined to a different location on the Armalite firing pin and the bolt has a bore for the spring.

That information might matter to a Gentleman who said he was considering an AR-10 firing pin.

Perhaps because I had to explain it to you, you were not aware.

FWIW,I say "45 Long Colt" but IMO,its OK.

Have a nice evening!

[stagpanther]

The firing pin "exerts force" only because it is carried along by the carrier--or is hit by the hammer. High pressure does not refer to anything the pin is doing; rather, it's referring to higher pressures internal to the barrel and chamber which in turn affect functions such as cycling, dwell-time, when the bolt unlocks etc. The cartridge you're dealing with naturally will have variable functioning as your pressures vary depending on the charge weights--energy yielded. Most of this will be "governed" by your gas system.

[tangolima]

Originally Posted by stagpanther

The firing pin "exerts force" only because it is carried along by the carrier--or is hit by the hammer. High pressure does not refer to anything the pin is doing; rather, it's referring to higher pressures internal to the barrel and chamber which in turn affect functions such as cycling, dwell-time, when the bolt unlocks etc. The cartridge you're dealing with naturally will have variable functioning as your pressures vary depending on the charge weights--energy yielded. Most of this will be "governed" by your gas system.

So "pressure" as in "high-pressure firing pin" refers to the gun's chamber / port pressure? That's what I first thought. But what does it have to do with the tip size? If I drop in a regular firing pin, it will screw up the action cycling? Can't wrap my head around this one.

-TL

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[tangolima]

Originally Posted by HiBC

He said he had an AR-10. Only Armalite makes an AR-10. If that means something different to you, the problem is in your thinking.



The DPMS is built like the AR-15 . Pull the retaining pin out of the bolt and drop the firing pin out.



The AR-10 ,pull the retaining pin,drop the firing pin out,but looky there! A firing pin rebound spring comes out! A whole 'nuther part!

I'd guess its there to lessen the firing pin impact on primers when the bolt slams shut.

And,to make up for the spring length,the shoulder positions are machined to a different location on the Armalite firing pin and the bolt has a bore for the spring.



That information might matter to a Gentleman who said he was considering an AR-10 firing pin.



Perhaps because I had to explain it to you, you were not aware.



FWIW,I say "45 Long Colt" but IMO,its OK.



Have a nice evening!

I did say ar-10 in op, even though I meant dpms, as I didn't realize the parts were different. Thanks for the info.

-TL

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[HiBC]

I'm not sure anything about post #16 is for me. It does not seem connected to anything I said.

I don't connect the firing pin rebound spring to gas pressure. Its about the inertia of the firing pin and those pesky little dents in the primer and military spec primers,etc.

I don't know what JP is targeting with this firing pin. If I had to guess,they are getting the jump on the new .277 military round that supposedly operates at around 75,000 psi. But thats just a guess.

The talented Gunsmiths of days gone by commonly bushed the firing pin holes in breeches when adapting older single shots of black powder days to higher pressure varmint rounds.
See if you can find a Frank DeHaas book on Gunsmithing single shots. Good stuff!
Note that in the 1911pistol the 45 ACP breech has a larger firing pin than 38 Super. 38 Super runs near twice the pressure a 45 runs.
Another step to adding a small tip firing pin might be replacing the bolt with one designed for the higher pressure . It would have a smaller FP hole and maybe some other upgrades for higher pressure.

This new military rifle 's normal operating pressure is proof load pressure for the typical cartridges we have been shooting.
Unspoken upgrades like alloy,heat treat,corner radii,etc might be part of the larger package.
But I have not been following it.

[stagpanther]

So "pressure" as in "high-pressure firing pin" refers to the gun's chamber / port pressure? That's what I first thought. But what does it have to do with the tip size? If I drop in a regular firing pin, it will screw up the action cycling? Can't wrap my head around this one.

Just google it--you'll come up with lots of hits on various forums that will explain it to you. Best of all--call your manufacturer--there's probably a very good reason they elected to go this route rather than try to pull the wool over your eyes with marketing hype.

[tangolima]

I googled and did it again just now. There isn't much useful really. 95% of the content is the "we are the greatest" type of advertisement / propaganda. That is why I posted here to ask.

Out of the 5% forum discussions is hardly anything relevant. Many believe 6.5CM has much higher pressure than .308 win so something high-pressure is needed. But both 6.5cm and .308 win have the same peak pressure of 62kpsi. All discussions on action cycling are related to rifle + 2 gas port, nothing really on the bolt or firing pin.

Digging into JP shows some hints. They have this high-pressure enhancedbolt, and the high-pressure firing pin should be used in this bolt. What makes the bolt high-pressure? 9310 alloy steel, as it will last 6x longer than the regular choice of steel.

There is one post on Reddit that seems to explain it more. The high-pressure enhancedbolt has better steel and smaller firing pin hole, so that primer crater is reduced. And regular firing pin's tip won't fit. Now that make sense to me.

I could well be wrong, as I'm still gathering info. I think that's what has been going on. AR-10 (I mean dpms), mostly LRP, uses the same trigger group as ar-15, mostly SRP. Weak hammer force over thicker firing pin tip means inadequate pressure (not chamber pressure) to indent LRP and causes misfires, especially with the reduced strength hammer spring for better trigger pull. Customers whine. Manufacturers have to do something. Small tips help, so they started selling high-pressure or enhanced firing pins. They should have bolt with reduced firing pin hole. Most of them didn't bother. JP did. The other guys just have undersized tips. Cratered primers? Don't ask don't tell.

Indeed one of the usual jobs for a gunsmith has been to fix sloppy firing pin in bolt. Bushing the hole or retipping the pin is the common approach. AR should work the same.

-TL

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[44 AMP]

While pressure is a form of energy and what we are talking about here is the energy delivered by the firing pin, I think the use of the word pressure is inappropriate.

Energy is measured in terms of pressure for some things, psi, ft/lbs, etc, but while a hammer striked with X amount of ft/lbs energy it does not "press" a nail into a board, or a firing pin into a primer. It strikes, or it drives, but it does not press. These are the conventions of terms we use and are widely and commonly understood.

I think use of "pressure" should be in line with the conventional useage, which in firearms, is normally a reference to powder gas pressure.

Another place where a different word is the usual convention is springs. Springs do exert pressure, but when talking about the force of a spring, the term usually used is "tension", not pressure.

Heavy impact, or high energy firing pin would be a more accurate and less misunderstood term, but then, I guess it doesn't have the attention grabbing pizzazz of "High Pressure".

[tangolima]

I don't know. The energy is the same, all come from the same trigger group, so can't call it high-energy.

I actually don't mind what they are called. I just want to understand what's behind the commotions. A side benefit is now I may have answer to why have been seeing so many range picked up brass have crater or even pierced primer.

-TL

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[tangolima]

I went measure the bolt and pin that give me cratered primers. The hole diameter is 0.079", typical dpms. The pin is enhanced, aka high pressure, firing pin from the same manufacturer. The tip has diameter of 0.075". It is sloppy. If the Fulton pins I ordered really have 0.078" tip as advertised, I will be happy. I don't worry about misfires, as I don't have a fancy trigger with light hammer spring.

For the future 7mm SAUM build, I will have to order kak's magnum bolt for $130. Can't find anybody else making it. I will see how well the 0.075" pin fits. If necessary I will fit the other 0.078" to it.

-TL

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[stagpanther]

Tango, you are saying several different things here which is hard to follow. It sounded at first like you bought a 7MM SAUM upper assembled--but now are saying you are doing a future build? So this upper you are having problems with--and are reloading for--is something else? If it came with a high pressure firing pin fitted into a conventional firing pin bolt then what is happening is the pressure upon the case face upon firing is forcing the primer to imprint into firing pin channel. This can cause several issues and will likely lead to malfunctions sooner or later.

"High Energy" has a specific meaning in the type of firing pin used. It is used in a bolt/carrier system designed to help enhance reliability and mitigate the effects of possible spikes in the pressure from the gas system when firing higher power cartridges.

Take a cartridge, lock the bolt back (and with the safety on and the gun pointed in a safe direction at something you don't mind destroying) drop the bolt on it and without firing it eject it. There should be a notable dent in the primer as a result of the free-floating firing pin striking it. So the firing pin has to successfully ignite the primer with that dent while at the same time not inadvertently cause a slam fire--or even a possible full-auto like mag dump.

Something like the SAUM I would not recommend as a first-time xx10 build. I would try a creedmoor first, because it will definitely entail system balancing issues that go beyond your typical 308 xx10 rifle without dealing with the additional complications of a magnum cartridge.

Try a 25 creedmoor--one of the most awesome high-performance new cartridges I've ever fired which will not beat you up in long shooting sessions--nor will it cook itself.

BTW--"high pressure" does not mean necessarily a cartridge that generates at or near absolute max pressure as rated by SAAMI/CIP--it can also mean a pressure higher than what the current rifle and gas system is balanced for.