About Cartridge Maximum Pressures

Ever since Newton and his laws of physics, professional engineers design structures to a load. It is interesting what they did before the laws of "equal and opposite" and "conservation of momentum". They basically guessed at things and operated by rules of thumb.

Mechanical structures are designed to carry a load. You can calculate load by multiplying pounds per square inch times the cartridge surface area in square inches. What falls out is pounds. Rifle chambers carry more load than the receiver as the surface area of the cartridge is greater in the chamber than the portion against the bolt. In revolvers the cylinder carries most of the load. The load path in revolvers is complicated, the frame carries some, the cylinder most.

Then there is duty cycle, how much load and for how many cycles. There are lots of one shot devices, things that only are supposed to work once. When they are used, their structure is so severely compromised that using them twice is unwise. Structures that are designed to last longer tend to be heavier and made of more expensive materials.

All firearms are designed to carry a load, at least the modern ones. Who knows what they did for design standards prior to the 1920's. Modern guns made out of modern materials are not expected to last forever. Even with standard loads there are design lifetimes. Guns will break at some round count. These things are generally not heavy enough to have an infinite duty cycle. You want to carry a 10 pound handgun and a 40 pound centerfire rifle?

You over stress the structure with loads that are above the design loads, don't expect your structure to last long. I have fatigue curves that show the lifetime of steel exposed to over stress situations. I would have to look, but I bet the overstress was a load close to or above yield. Anyway, you overstress a part, the lifetime of that part is radically reduced. Something that might be expected to last 10,000 cycles, might fail in 600.

This post, on another forum, it is worth looking at the fatigue curve, and the blown up Ruger pistol.

Fatique Life of 4140 steel

http://castboolits.gunloads.com/showthread.php?150409-Ruger-om-44-convertible&highlight=convertible

Just a few thoughts on this. For Background I am a mechanical engineer with a heavy background in failure and fatigue.

I wonder if I could request a high quality photo of the fracture zone of the cylinder? I am specifically interested in the grain structure of the bolt notches.

I put fort the following.

1) Firearms in general (the type we plebeians can get our mits one) are not designed for infinite fatigue life.

2) The Factors of safety used in firearms design are in line with low end of fatigue requirements (usually less than 10,000 cycles).

3) One of the funny things about fatigue is that each time you push the material past its original design point, you lower its expected life.

4) I am looking at this as an older gun with an unknown number of rounds through it. but based on its age a substantial round count seems likely.

5) When these firearms are designed it is generally preferable for something else to go before the cylinder lets go and takes the top strap. Generally this takes the form of the gun wearing loose or the barrel wearing out. But they are designed to handle X rounds at standard pressures.

6) I see alot of folks calculate the strengths of Rugers, but these calculations are only ever performing an evaluation on a straight static pressure basis. This is wrong when trying to determine if a load is safe.

I attached a couple of marked up figures for your perusal
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I don't think it is any coincidence that the SAAMI proof loads to max average load ratio is similar to ratio of threshold of plastic deformation to the fatigue failure stress at a number of cycles approximately the max number of times a gun might be fired.

That's right, I am saying there are signs of intelligent design at SAAMI.

FatigueSN-1.jpg

10 or 12 years ago some guy working in Boeing structures drew this plot for me in relation to Rem700 bolt lugs. I don't think he copyrighted it. I know I have not.

10,000 stresses at 70% of yield stress reaches fatigue.
SAAMI proof loads for centerfire rifle are between 1.3 and 1.4 times the max average working pressure = 77% ~ 71%.
Coincidence? I think not:o
 
Why are cartridges rated to a maximum pressure if the main thing you should worry about from loading over max charge is the gun blowing up? Shouldn't the guns themselves be rated for that pressure? Can you go slightly over a maximum pressure for a given cartridge as long as the gun can handle it? Or are all guns rated to the maximum pressure of the cartridge they fire?
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First off, lets be clear on a couple things. The pressure ratings of cartridges, the SAAMI "max pressure" for any and every round is NOT the same as the blowup point of your gun. It's not even CLOSE!!!!

It is the max WORKING pressure of the round. Their max standard for what every properly built gun in that caliber should take, WITHOUT damage, and without undue wear, for the expected life of the gun.

In every pressure system, there is a significant difference between the max allowable working pressure, and the maximum containable pressure.

The reason the pressure limits are so much lower for some cartridges than others is mostly a matter of age. A great many rounds existed well before SAAMI, and their standards. What SAAMI did was to adopt a standard for them, based on the general level of pressures normally found AND the guns commonly chambered for them. Rounds originally loaded with black powder, which could, when loaded with smokeless powder, be much higher pressures, were given a pressure standard matching black powder pressures.

Again, due to the majority of arms (already existing) for those rounds. Your 17kpsi .38 Special load is intended to be safe in ALL .38 Special guns. Guns made to different standards than guns made for the .357Magnum, though they might appear identical to the eye.

Many older guns were NOT made with much more strength than needed.

It is a somewhat flawed comparison, but think of the SAAMI pressure limits as the red line on your tachometer. Can you run your engine over the red line? Sure. Does it instantly blow up? NO. WILL IT, if you keep doing it? YES.
 
I was reading at a tenth grade level in third grade, never wrote anything that earned less than an A, had two essays submitted to an arts journal when in art 101,have had a number of short articles published in glossy print, and made a living for years editing garbage into eloquent prose.
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Sorry, I was born with a copy the Iliad in one hand and War and Peace in the other (darned crowed in there!)

Sadly no one saw my brilliance and published me.
 
I have to go with 44AMP. I pretty much use Hornady load books. They list loads for older rifles, loads that should only be used in modern rifles, load reductions for older rifles, loads for modern reproduction rifles and so on. Even factory ammo has +P loads. It is not an absolute thing.
 
The reason the pressure limits are so much lower for some cartridges than others is mostly a matter of age. A great many rounds existed well before SAAMI, and their standards. What SAAMI did was to adopt a standard for them, based on the general level of pressures normally found AND the guns commonly chambered for them. Rounds originally loaded with black powder, which could, when loaded with smokeless powder, be much higher pressures, were given a pressure standard matching black powder pressures.
Click to expand...


For old historical rounds, SAAMI pressures reflect the metallurgy and technology of the times. Many old firearms were made before vacuum tubes, and I am certain very few readers of this have ever seen a vacuum tube and understand what a primitive state of technology that was. But even so, vacuum tube technology was much, much more precise than the human senses of taste, touch, smell, and vision.

I am of the opinion that CIP pressure standards, that is European pressure standards, are higher for certain cartridges, such as the 8mm Mauser, is primarily due to the fact that European sellers must submit their firearms to proof before sale.

I am basing my information on the book The Standard Directory of Proof Marks by Gerhard Wirnsberger. I am ashamed to admit that I bought this book in 1988 only for the proof mark pictures, so I could date firearms by proof marks, and I did not read the test until recently. The text was quite interesting in its own right, the author really knew German proof laws, and from the book, there are reciprocal agreements between EU Nations. That is, all these Nations had to raise their proof standards to an equivalent standard, for Germany to recognize Finnish proof marks, for the French to recognize Germany proof marks, for Austrian proof tests to be recognized as valid by the Finns, French, Germans, etc, etc, etc. I knew that firearms regulation was different in European countries, I sort of knew of Proof Houses, but that was about it. While I hardly know anything about individual EU country firearm laws, but according to this book, all European firearms have to be proofed before sale. In the US the manufacturer proofs the firearm once. The firearm may be out on the American civilian market for 150 years, pass through a hundred owners, bought, sold, stolen, but the firearm is only inspected for soundness by the manufacturer once. In Europe, every time that firearm is sold, it has to pass through a proof house. So if the firearm had 100 owners, it would have been proof tested 100 times. The book states that the proof marks of various American manufacturers are not accepted as valid in Europe, so newly made American firearms have to be proof tested before they can be sold in Europe.

If I am wrong about this, if the laws have changes since 1988, I would like to know.

American’s know that American proof testing is that some sort of an overpressure round is fired in the firearm. We actually don’t know that, American manufacturers may not be firing overpressure rounds at all but I do know that some manufacturers function test their firearms. I actually don’t know for certain what any American manufacturer does, I assume they function test, I assume they fire an overpressure round, and I assume that a Quality Assurance Specialist gages the chamber, barrel, etc for compliance to standard. But, there is no proof law in the US and some manufacturers may be doing nothing more than boxing the guns with a warranty card.

As for what a European Proof House does, based on what I have read a European Proof House does more than just fire a round in the firearm. They gage the firearm. I recall reading they gage the chamber, barrel dimensions, and probably conduct a number of extra inspections. I assume they function test every feature, such as safety and trigger. This is conducted before the live fire test. European proof testing is conducted with a cartridge that produces 30% more pressure than a standard cartridge. For the test to be valid, they lubricate the cartridge. Parasitic friction results when a dry cartridge is fired in a dry chamber. This parasitic friction between case and chamber reduces the load on the locking mechanism. (It also stretches the case) Lubricating the cartridge fully loads the locking mechanism. This is important, the Proof House is the one certifying that the mechanism is safe, they don’t have a financial interest in selling the firearm, they do have a financial interest in protecting their reputation. If they did not lubricate the cartridge they would be rightly criticized, perhaps sued, for an inadequate test of the locking mechanism. They would not be able to certify that they loaded the mechanism 30% over standard loads. NATO EPVAT testing specifically calls out the testing of firearms with an oiled proof load as the final test see: https://en.wikipedia.org/wiki/NATO_EPVAT_testing


American’s just assume Proof Tests are free or ignore the issue. Based on what I found on the web, the British proof house charges today it costs ₤30 for a shotgun, ₤25 for a centerfire, ₤15 for a rimfire rifle or barrel to be proofed. http://www.thefirearmblog.com/blog/2014/08/29/show-proof/#sthash.xKe1BcBu.dpuf I thought it would be more.

What is not mentioned is what happens to a firearm that does not pass proof. For one thing, it can’t be sold. According to my book, in Germany, prior to 1968, guns which failed proof, for whatever reason, were destroyed by smashing or cutting. This must have been fun for the Proof House workers, smashing an otherwise perfectly good firearm because the safety failed. After 1968, only the bad part are given a rejection mark.

It is clear that one intended effect of European proof laws is to reduce the number of old, antique firearms in civilian hands. Old firearms are tested against current standards, current proof pressure cartridges. Old firearms, worn out firearms, that do not meet proof cannot be sold. I don’t know what the owner does, maybe he can sell parts off it. This is a financial risk to the owner, I am very certain the buyer expects the owner to pay for the cost of proofing. In time, old, structurally insufficient firearms will be weeded out of the system, either by rejection by the Proof House, or by owners deciding that the risk of failure is such that owning or modifying an antique is just not worth the financial risk.

For cartridge manufacturers, for countries with aggressive and universal proof test systems, they know that the population of firearms out in the market have been tested to the latest pressure standards and therefore can handle full power loads.
 
I don't think it is any coincidence that the SAAMI proof loads to max average load ratio is similar to ratio of threshold of plastic deformation to the fatigue failure stress at a number of cycles approximately the max number of times a gun might be fired.

That's right, I am saying there are signs of intelligent design at SAAMI.

FatigueSN-1.jpg


10 or 12 years ago some guy working in Boeing structures drew this plot for me in relation to Rem700 bolt lugs. I don't think he copyrighted it. I know I have not.

10,000 stresses at 70% of yield stress reaches fatigue.

SAAMI proof loads for centerfire rifle are between 1.3 and 1.4 times the max average working pressure = 77% ~ 71%.

Coincidence? I think not
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Clark: I may steal your image and your analysis because it is dead on. I will at least plagiarize. Good poets borrow, great poets steal. Thanks for making clear something I suspected. :)
 
The guy who made that image for me calls himself Jon A.
He posts here and there. He is a long range hunter in WA state.


I hope he did more that write in red on a page from his text book.
Ah, he is a workaholic. He probably wrote a section in the Boeing design manual on this topic.
 
The guy who made that image for me calls himself Jon A.
He posts here and there. He is a long range hunter in WA state.
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There are a number of SN curves, could be one for each material. You can imagine that running tests that require millions of rotations at each stress level would be not only tedious, but expensive. Somewhere I have one for 4340 and low carbon steels. The one you provided does not mention which material but still, it is useful.
 
So what I'm getting from all of this, is that maximum pressures aren't there because your gun will blow up if you exceed them, but so that you don't wear out the average gun chambered in that caliber excessively, among other things.
 
The SN curves for Aluminum alloy go to zero.
Don't keep flying old Boeing jets forever.
But the steel valve springs in our cars never seem to die.
 
So what I'm getting from all of this, is that maximum pressures aren't there because your gun will blow up if you exceed them,
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No, the guns won't blow up if you exceed SAAMI max cartridge pressure BY A LITTLE BIT!! IF you exceed max by a lot, then yes, the can, and will.

Generally speaking, until you reach the point of blowing up your gun, you will get case failure BEFORE you get a blow up failure with your gun. Even properly supported brass begins to fail or does fully fail in the 65-85k psi range. (many variables), and failed brass means gas pressure going where it isn't meant to go, and DAMAGE can, and often does result. Damage, not blow up failure of the gun.

However there are too many variables involved to give more than the most generalized statements. Each and every gun & ammo combination is slightly different. Most fall in the middle of the curve, but some are at each end.
 
If you approach it at reasonable increases, you will get a bolt jammed (bolt gun of course)


That said I saw a modern Winchester 70 get blown up last year.

Barrel went out 15 ft, receiver blew open the top, scope lifted off and flew back.

Guy lost some teeth but otherwise ok, guy standing next to him got hit with some shrapnel in the cheek, good thing not an eye.

Gun was being tested for another person and it looked like reloads involved.
 
So what I'm getting from all of this, is that maximum pressures aren't there because your gun will blow up if you exceed them, but so that you don't wear out the average gun chambered in that caliber excessively, among other things.
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For the most part, yes. The SAAMI or CIP max pressure also assures that ammunition made by any manufacturer should work in any firearm made for that cartridge, with a few exceptions. The M1 Garand is a famous exception because the gas system requires a specific port pressure and because of that has a pretty narrow powder burn rate range for normal jacketed bullets.

But "port pressure" and "max average pressure" are two different things, and you can destroy a Garand with a SAAMI spec "max average pressure" load that fails to also meet the "port pressure" standard necessary for the Garand to properly function. So it is relatively easy to destroy a firearm without going over MAP.

In a bolt action rifle, there is no port pressure issue to worry about. That is why NSWC Crane upped the MAP in the Mk248 Mod1 round, a 300 Win Mag pushing a 220 SMK over 2,900 fps. The military is only ever going to run that load through bolt action sniper rifles, so having a MAP of 68,000 psi is no problem, especially since the military doesn't reload. That would be a bad thing to do for a 7.62x51 sniper round though, since it would have to be spec'd to run through an AR10, M14, as well as bolt action rifles.

Hope this is food for thought.

Jimro
 
So what I'm getting from all of this, is that maximum pressures aren't there because your gun will blow up if you exceed them, but so that you don't wear out the average gun chambered in that caliber excessively, among other things.
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There is a very good reason no firearm manufacturer recommends reloads and explicitly states the warranty is void if used with reloads. Reloaders don't have pressure measuring equipment, many don't have the slightest idea of risk, or are infact, risk takers. Gunpowder has an exponential pressure curve. Studies have shown that humans think in linear terms so we humans don't have an appreciation of the risks associated with exponential systems. Exponential systems go out of wack very fast.

This rifle was a Commercial FN Mauser in 264 Win Mag. The typical guy who wants a Magnum wants a fast round. In my opinion, this owner over loaded his rounds and probably cracked the lugs in less than 500 rounds. He would have shot out the barrel in under 1000 rounds, I have talked to 264 Win Mag owners whose barrel keyholed around 700-800 rounds. Cracking bolt lugs may not have blown up the rifle, but if the rifle had been fired with cracked lugs, it is likely it would have blown up.





Here, the load on the bolt lugs did not cause cracks, instead an overpressure round blew the case head, and the receiver ring gave way. What is forgotten by , Fools, Nuts, Hatcherites and Ackleyites is that the case is a lot weaker than the action and if the case goes, all sorts of unpredictable hell breaks loose.







Not everyone has a good sense of risk, there are people who are fearless, they push the boundaries, keep on pushing, they have a sense of invincibility and they want the excitement. These people are outstanding candidates for this list of BASE jumpers:

BASE Fatality List http://www.blincmagazine.com/forum/wiki/BASE_Fatality_List

I am not going to splat myself against some rock wall, or try to drive my head through a tree at 200 mph. But for those who want to push boundaries, how about taking up the sport of BASE jumping?
 
264 Win Mag. Came from the factory with a short throat and two diameter 140 gr bullet. Using standard 6.5 mm 140 gr bullets loaded out to factory OAL and trying to reach factory velocity is a recipe for disaster.
 
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