Following on from the gas venting thread, I thought I'd better start another.

How much pressure is required to blow a primer? SAAMI list 65 000psi as the safe max pressure for cartridges, but when a primer does blow what was the pressure to do it? 70 000, 75 000psi?

I was wondering how much leeway/safety margin lies between 65 000psi and blowing a primer.

On another forum, a bloke gets 3 400fps with a 100gn bullet in a .257 Roberts and over 3 000fps from a 140gn in a 7x57. He has never reported any issues like blowing primers. If he's exceeding 65 000psi, how much more pressure till something gives?

I thought one of the gun writers might have seen pressure data indicating when primers will blow.

Interesting.

My experience is that pressures up to 70,000 or even 75,000 PSI often don't show conventional pressure signs--though that obviously depends on the brass and primers.

I have only managed to blow primers a couple times over the decades. Once was when my balance scale was inadvertently moved to a charge around 10% higher than the charge I'd worked up to. A general rule is that a charge of single-based rifle powder (and this was a single-based powder) results in approximately twice that much increase in pressure. So if my load averaged 65,000 PSI, the overload would average around
80,000 PSI.

I shot it on an average summer day, and the only sign of higher pressure was the chronograph reading, which was about 10% higher than normal. This is about what single-based powders does when the charge is changed: Velocity follows the percent of increase or decrease. Of course, I thought the chronograph was being screwy, and since there were no obvious "pressure signs" otherwise, I shot another round. About the same chronograph reading, and a little harder extraction. (The rifle was a Ruger No. 1.)

On the third shot the primer blew, probably because the barrel has warmed up. At that point I finally suspected the chronograph wasn't screwy, but I had somehow screwed up. Took the rest of the rounds home, pulled the bullets, and weighed the charges, finding the 5-grain "overcharge."

MD, just curious if you checked for extractor marks on the case head of those rounds?

I've pushed a few to the point of extractor marks, but only blown a primer once.

He said it was a Ruger No. 1

I think you meant to say ejector and No 1's don't have 'em

I've blown one. Ruger No. 1 also - 180 gr bullet in a .30 Gibbs ('06 super improved) using RL22. Chrono read 3,150 fps. Primer fell right out.

I had shot this load before. Dumped that bottle of '22 lickity split and have never used the stuff again.

Well, that would explain why he didn't check for extractoor marks.......

Ackley experimented with blown primers.

His test equipment was a copper crusher setup, so his results were actually in what we now call CUP. But, as was common at that time, he reported them as PSI.

Doing the necessary units conversion, he found that primers start falling out around 80 KPSI, which is consistent with MD's result.

My testing has shown about the same. A chamber cut to spec, and an action machined for a correct casehead to boltface interface, pressure in the mid 70's didnt show anything.
Charlie

As Mr. Sisk and others have noted if all things are right then...

I believe that I had a blown primer on a rifle that I purchased on-line and the firing pin looked like a flat punch with sharp edges. I am pretty sure that the pressure wasn't the cause for the blown primer. I replaced the firing pin and had no further problems. I suppose that there are other things besides pressure alone that will cause blown primers.

I'm not an expert as some others are that have answered this thread, so take my comments as my two bits.

It's not the same for all primers. This isn't a rifle-specific area of the forum, so I'll add that I don't think standard pistol primers will take 80kpsi or even 65kpsi. Magnum pistol primers or non-magnum ones with a thicker cup (Remington 5 1/2) can take over 50kpsi in cartridges like the 5.7x28, but higher pressure cartridges like the 454 Casull (65kpsi) are specified with rifle primers. I don't know what the ultimate limits of pistol primers are, but I (unintentionally due to a scale use error) fired some standard SPP at a pressure that Quickload calculated to be somewhere between 51 and 53 kpsi. The primers were bulging and cratered with a sharp metal ridge raised around the pin dent. They were not flat, but ballooned out. They probably would have been fine if they were thicker magnum pistol primers, but as it was, the cup must have been close to failure. By close, I think another 15kpsi would have resulted in rupture.

There are different things that people call "blown" primers....

1. The primer pocket expands to the point that the primer falls out. Had a shooter at our range that experienced this with factory loaded 270 ammunition.

2. The primer flows out of the pocket excessively.

3. Cartridge pressure causes the firing pin dent in the primer to invert, forming a bubble instead of a dent. With just a little more pressure, the bubble cracks around its base and falls off, leaving a "pierced primer", which isn't really pierced at all. The bubble then often falls into the mechanism. This can happen in an AR15 that is firing 5.56 level loads that use standard small rifle primers.

4. An oversize firing pin hole allows the formation of a crater around the firing pin dent in the primer.

5. Propellant gas leagage around the primer.

Ackley's experiment was with #1.

So how much pressure is needed to blow up a modern bolt action rifle? If primers go POP at 80 kpsi how much more pressure is needed to destroy the action?

I've had primers fall right out of numerous different cartridges in several different rifles. Some (mostly 300WSM's) were factory loads, some were loads on the edge, and some were baffling. When I was shooting a 6x47 for short range BR (for those who don't know, the 6x47 is the 222Mag necked up), the best accuracy was a load which loosened primer pockets pretty quickly. On a hot day, I would occasionally drop a primer. In my 256 Newton, a load which should have been fine, suddenly blew a primer. I later found that I was having trouble with powder hanging up in the measure and I suspect I had one light charge followed by a heavy one. My carelessness. This was in a Model 54 Winchester and I was happy not to have gotten any gas in my face. As it was, there was a puff of smoke and that was it.
I have loaded rimmed cartridges (303 British and 30/40 Krag) damned hot and have not blown a primer. I have some thoughts on this but they're just my thoughts and may have no relationship with reality. GD

I thought the size of the primer hole in the case also affects the pressure/force seen by the primer. I realise the difference between pressure and force BTW.

I've only seen pierced primers (faulty primer), leaking primers and experienced loose primers (was a batch of undersized Winchester ptrimers). The leaking primers were in Winchester factory 8x57 ammo (oldish unmarked blue box ammo) that eroded the bolt face - someone elses rifle.

I haven't persnally experienced blown primers and assumed the term was more often used for overpressure loads and case head expansion. The pierced primer was bad but not catastrophic.

I've had two primers to pierce in twenty five years of reloading. They were Remington 9 1/2 primers. My friend was using the same lot of primers and he had a primer to pierce.

I don't know exactly where that demon lives, and I don't want to experimentally find out. It's a lot, though.

Just as a reference point, the US Mint puts 160,000 PSI pressure on the steel dies used to form high grade coins. After many uses, they do tend to crack.

So what's the point of pushing a load to that level ? Wrecking your gun ? Getting hurt ?

Depends.....

I realize that's not a popular answer but what you're describing could depend on a number of factors, such as, the peak maximum pressure, the maximum average pressure, the condition of the primer (thickness, quality of material), the firing pin (I've seen folks sharpen their's for better ignition 😵). The quality and/or design of the action or chamber, any strange restrictions (i. e. really tight chamber, no free bore, etc...)

So it depends.

Going back to your original post you used 65,000 psi as an example but if you look at the SAAMI spec sheet for centerfire rifles you'll see that SAAMI rifle chamber pressures vary with cartridges and so the proof loads also vary.
https://saami.org/technical-information/ansi-saami-standards/

On page 352 you'll see how SAAMI goes about "proofing" cartridges for safe use. The basic rule of thumb is between 1.3 to 1.4 times above your safe load. For an example, if your rifle load lists 50K psi as a max safe load then it was probably Proofed at 65-70K psi. Don't try and find out when it will explode because there's a lot of variables that will be different for every different rifle/cartridge combo you run into. That's why having standards is good.
Remember, safe loads are designed to last the life of the barrel, going higher will certainly shorten the life of your barrel and possibly put you in danger. Stay safe 👍

Cowbell,

Actually, SAAMI maximum average pressures (MAPS) never exceed 65,000 PSI in any cartridge, though quite a few rifle rounds have lower MAPs.

65,000 was established as the maximum for ANY round not to increase barrel life, but to ensure that outside factors (primarily warmer temperatures" wouldn't cause pressures to rise to dangerous levels. Even with the most temperature resistant powders made today, higher temperatures cause pressures to rise, whether the heat is a result of amient temperature or a barrel heated-up by firing. The pressure-rise is less than with "standard" powders, but still rises. If the round gets hot enough, pressures can indeed rise enough to cause several problems--but barrel life is not a consideration.

Then there are tougher primers than most. I bought a couple thousand CCI No. 34 Primers for 7.62mm Ammunition (Yeh, I know a fancy military 308)

They are supposed to have a tougher cup. They were tougher, I understand because of unintentional firing of ammo when an AR slams the bolt shut. But I'd think they would also take a higher pressure before they would vent.

We ran tests on blowing up rifles (in a blow up chamber). There is or was back in 1969, a big difference on what different pressures different manufacturer's rifle would take.

Blowing up rifles was one thing, escaping gases that would shoot back into the shooters face was another. At that time all rifles were not equal in that regard also, I believe that they still are not.

If I were interested in getting the highest velocity (highest pressure) out of a certain cartridge I certainly would be choosy on which manufacturer's rifle I'd use.

But that isn't me! If I want more velocity, I use a larger cartridge.

The other thing I'd like to add about high pressure is temperature sensitive powders. I've had real bad luck with some powders in heat after developing in mild temperatures. High temperature with heat sensitive powder can cause blown primers, gases in the shooters face and damaged rifles.

Just to clarify. I never started this thread with the idea of pushing hand loads to crazy levels to squeeze out a bit more velocity.

More so that I wondered when a primer blows a few inches in front of your face what the pressure went up to. From the posts above it seems around 80 000 psi seems to be where primers will POP. Others have stated how they have fired loads around 75 000psi with no noticeable pressure indications. That doesn't mean I'm going to push my handloads up to 75 000psi.

A blow up chamber? Did you put a blow up doll in there to pull the trigger?

It seems to me that one of the key factors is how much support the primer has. For example, if the primer is hard against the bolt face, and headspace is tight so the striker can't drive it forward off the bolt face, and the firing pin is tight in its hole in the bolt face, with a wide surface area, and more or less blunt, then the primer's effectively able to transfer the stress to the bolt face and striker, and is not carrying much stress itself.

Change one or more factors and you change the stress distribution. For example, if there's a lot of clearance around the firing pin there's a portion of the primer not only unsupported, but an appreciable stress concentration in that annular area. Similarly a pointed firing pin creates more of a stress concentration.

FWIW I've had the odd few primers primer let go in circumstances where one or more of these factors is in play, even with loads which aren't all that hot. I haven't gone out to try to test this hypothesis experimentally though, in any more rigorous way, as I'd prefer not to be popping primers if I can avoid it. .

One of the easiest ways is to just use the barreled action, drill a hole in a tire, stick the barrel thru the hole with the action tucked inside the tire opposite the hole. You need a second hole for the lanyard tied to the trigger.
Best to park your buddys nice pickup between you and the gun before pulling the string.

Be carefull of case welding that can take place on handloaded ammo that has been sitting a couple years.
The bullet can weld itself to the case, which will increase the pressure enough to lock up a gun and blow primers even with safe level loads.
Best to test the ammo first before firing it by turning the seating die adjustment a turn or so and listen for a snapping sound as you reseat the bullet deeper.

The bullet cannot weld itself to the case that is impossible. Corrosion is not welding

Actually, bullets can indeed weld themselves to cases. It is a quite well-documented phenomenon, an example of diffusion bonding. Diffusion bonding has industrial applications too - I've done some work with these. You really just need two pieces of material of fairly similar composition (such as a gilding metal jacket and a cartridge brass case neck) in good intimate contact without anything between them (ie both nice and clean), a bit of time. Temperature also helps, but it is a solid-state process. Atoms essentially wander about, and end up crossing the boundary (if conditions are right) and taking up positions in the crystal lattice of the other piece. If enough atoms do this the boundary becomes sufficiently blurred to make quite a good bond. It is not a corrosion process.

Never thought of that, darn. We used a string.

Welding makes more than a bond welding makes the 2 pieces one. The brass would be ripped apart if actually welded

It is not welded no matter who claims it to be just as soldering isn't welding

Dan-oz is correct in his explanation of the bonding.

Bonding isn't welding

If you put two gauge blocks in contact for a few seconds, they tend to stick a bit. If you smooth them enough and put them together in a vacuum, they fuse and become one. Bullets weld themselves into cases, same process, takes longer.

Diffusion bonding or diffusion welding is a solid-state welding technique used in metalworking, capable of joining similar and dissimilar metals. It operates on the principle of solid-state diffusion, wherein the atoms of two solid, metallic surfaces intersperse themselves over time.

I think the confusion here is between fusion welding and pressure welding.

https://www.brighthubengineering.com/manufacturing-technology/30578-types-of-welding-processes/

But somehow I think the greater concern would be due to the stickiness from corrosion. Not saying a solid state weld couldn't form just saying I'd worry more about corrosion and would do the seating die check before firing any suspicious ammo that's been lying around for many years.
https://forum.accurateshooter.com/threads/bullet-weld.3964549/page-2

Anyway, either one would probably raise pressure levels.

If actually welded the bullet would tear the case neck away to break free

When you test this for yourself do NOT use federal brass... historically the heads are soft and you get loose primer pockets that change the results drastically.

But I found the same as MD and Charlie...

Many years ago I loaded a box of 20 243 cartridges. I used new Remington brass and a load of IMR-4831 that was roughly half way between the starting load and the max load having worked up from the starting load. Everything went smoothly until shot number 18. I was struck in the face (left hander shooting a push feed M-70) by a large sliver of brass; lots of blood. The bolt had to be beat open.

I later pulled rounds 19 & 20 no abnormalities noted in the charge weight. No issues with the rifle after being checked by a gunsmith. The only thing I could come up with was a soft case head... Still don't know what caused the severely blown primer, but the case has sat on my reloading bench for many years as a reminder.

Bottom line, the previous seventeen rounds everything appeared to be normal and then it wasn't...

I have actually examined diffusion-bonded joins under the microscope, and done physical tests to the strength of the bond, and they definitely do meet your definition. There is also a fair bit of evidence out there for the phenomenon in cartridges.

Absolutely correct.

My fellow metallurgists seem to agree that diffusion bonding is welding. On what basis do you say that it is not?

Winchester primers are typically softer, and flow, resulting in the piercing mentioned by Denton above.

You will never pierce a CCI primer, they will always blow.

Federal primers will actually flow back into the firing pin hole in the bolt face giving a very distinct artifact on the primer.

In general, all else being equal, typically Winchester primers will pierce before CCI's will blow.

[/quote]

Winchester primers are typically softer, and flow, resulting in the piercing mentioned by Denton above.

You will never pierce a CCI primer, they will always blow.

Federal primers will actually flow back into the firing pin hole in the bolt face giving a very distinct artifact on the primer.

In general, all else being equal, typically Winchester primers will pierce before CCI's will blow.
[/quote]

That's been my experience as well.

One of the interesting things I've learned in talking industry people is the CCI 41 small rifle primer--the one designed for AR-15 and other semiauto .223/5.56 loading--doesn't actually have a tougher cup, as many would assume. Instead the "geometry" of the cup and anvil is changed from the standard CCI 400 SR primer is changed.

Yep, MD ‘s dead nuts on what I experienced over time.

I used to use winchester primers religiously...they are the only one’s I’ve had pierce.
them moved to remy benchrest, tried some federal and was suprised at it...

Finally made the jump to CCI and provided they are available I’m happy.

You may have witnessed the pressure excursion that the 243 is infamous for, especially if the throat was worn. My theory is it is due to the powders used, at that time some type of bulk powder similar to 7828 and to throat wear and variations. The same thought on the 7RM which had the pressure reduced after it exhibited greater than acceptable pressure excursions. I have loaded many hundred of these two rounds and not witnessed this phenomena. The 243 was plenty worn and the 7 RM I shot the barrel out at around 3,000-3,500 rounds. It was probably gone before but this was at the point it started to shoot erratically and larger groups across the board.

I believe what Charlie Sisk was saying is that a tighter chamber doesn't show pressure signs or blow primers as soon as a looser chamber would. Is the Ruger Number 1 considered to handle pressure well and not show indications as much? I was getting flat primers with a #1 thought it was pressure but turned out to be tight primer pockets on new Nosler brass, the primers were getting the final seating when chambered. When shot they backed out some and were flatter than they should be. But an unfired round looked flatter too after clambering.

I've pierced a CCI primer, and blown a primer...

They do handle pressure well. My pressure sign is when the extractor fails to extract (slips over the rim) and I have to pry the case out with a screw driver.

You can also often knock a stuck case out of a No. 1 Or other falling-block SS) with a stout cleaning rod of the right diameter.

Leaked primer on my 700. Greg Tannel did the repair. This was not from high pressure. I was getting cratering at min loads due to the over sized firing pin hole. I lived with it until I took a leak. .257 Bee, Bartlein barrel Federal GM215M primers. First time that has happened. Zero pressure signs.

Had a couple of Winchester LR do the same as the above in a mildly loaded 257 Roberts.

15 or so years ago I got a deal on 1000 Rem 9 1/2 primers. I loaded a bunch of '06, 243 and 22-250 ammo and went shooting. I got several (many) pierced primers as pictured in the above post. All 3 rifles were affected. I wrote Remington and they wanted primers of the lot I used, fired cases and unfired cartridges. I sent them out and got the reply that since they had no control over the storage or use of said primers, I was SOL. So no answer and no more of my money spent on Remington components. All rifles have pitted bolt faces but otherwise perform well.

I had a CCI primer blow in the 9.3x62 using 66gr of big game in a Lapua case with a 286gr Partition. I subsequently performed a node test and discovered that I basically stopped gaining any velocity beyond 64.8 grains, so that's what I use now and have not had any more problems.

This is the same results I've had, I had a load I shot for years that was fast, but you could load the cases 7-8 times, nothing looked out of the ordinary, when I got a pressure trace, they averaged 68k psi with some up to 71k. I backed it off after that. I think it takes 80k psi to blow a primer as a rule, and my one blown primer was just like MD, 4th or 5th shot when it was hot and I left it in the barrel for a while before I shot it and let it heat soak really good.

Just for fun I went looking for bond strengths.
An average Ni-Ni bond was reported at 81.75 (didn't see the units)

Tin-Brass alloys are somewhat more difficult to find...
I wonder if the nickel plating on CCIs results in a more catastrophic failure as a result of a slightly higher bond strength than the underlying brass.

Just supposing...

Edit:
More digging and Capitalcartridge.com posts a factoid that nickel coated brass is more fragile or brittle.

That would suggest a more dramatic failure mode...

For what it's worth.