I finally ventured out into the cold and fired three shots with a new pressure trace strain gage system. For years I've used a heavy load of H414 with a 160 grain Nosler as a standard load that goes over 2800 fps. This load has been hunted in 100-degree weather and shows no pressure signs in any of the conventional ways. Cas head expansion, cases fall out of the chamber, primers not flat, no bright spots in the extractor area, primer pockets never get loose until 8-9 reloads. Several of the others here use a similar load with H414. I think this load proved right away how inadequate the conventional methods are, as the pressure reading was over 70000 psi on all three shots. Now bear in mind that the SAAMI specs for 6mm Rem and .257 Roberts when converted from CUP to PSI is about 64000 psi, so the pressure was not ridiculously high, but surely will need to be backed down some. I've been using the usual methods for years, only blown one primer in 34 years of reloading, so never had any problems, but this really opened my eyes. I guess I'm going to have to go in and load some more shells at least 1.5-2 grains less H414 and try them in the Ruger. The 100 fps velocity loss won't be noticeable to anything you shoot and I'll check the pressure on them then. I guess now that we have technology available to use a strain gage system, everyone should try it, especially if they push the limits or load some unusual calibers with a limited amount of data available. Obviously some loads that appear normal by all conventional estimates can be considerably too high in pressure.

Very interesting. You said you were in the "cold" for this as well. I'd be curious to hear what the psi was at 100 degrees.

It is often too easy to get obsessed by that "extra 100 fps", even when such a slight difference is meaningless in application.

Thanks for posting your results. This is the kind of info that keeps us from getting into trouble, or allows us to back out before something horrible happens. The 7X57mm loads I've been using for thirty years "seem" OK also, but I have no idea what pressures they would show if measured on your equipment......

9.3x62, Although it was cold this weekend, I left the computer and rifle in the truck, so actual temperature was probably 72 degrees, didn't know what my laptop would do at 0 F. From chronographng loads, I can tell you that getting a barrel hot, then leaving one in the hot chamber for five minutes and firing it will raise pressures more than 100 degree weather. I've seen the velocity jump up over 100 fps if you leave one in the chamber for a while and let it soak up that barrel heat, so I am sure the pressure will go up as well. I don't know how heat sensitive H414 is, but the pressure had to be higher in Namibia, and they still functioned perfectly.

Velocity itself can be a big help to determine pressure, with barrel length taken into consideration. After all, theres no "free lunch".

If you look at loading data for the .280 rem, you will see that it has a hard time making 2800 fps with 160 grain bullets, so the 7x57 should have an even harder time.

I know what you mean about conventional pressure signs. I used to load hot until I bought a copy of Okshooters .30-06 manual. None of his loads showed any pressure signs at 70,000 psi.

This lead me to conclude that the reload manuals aren't lying.

Is the sky falling? Some also warn of metal fatigue.

It seems to me that the rifle has been holding the load for a long time. On the other hand the load is seems to be maximum on that particular rifle. No mention was made of the case head expansion on new brass.

I really don't load very hot. I think I will forgo the pressure trace. It's easier to just use a larger cartridge.

jstevens...

I did a multifactor experiment, and found, as you have, that barrel temperature is more important than ammunition temperature... approx 3X as important.

It's a good idea to monitor barrel temperature if you want best results. I strap a thermocouple to my barrel when I want the most precision I can get.

Denton, I noticed the big changes in velocity due to a hot barrel years ago, so I haven't made any attempt to see how much the pressure changes, as I know it is considerable due to a huge velocity change. I was chronographing some loads, and just left a round in the chamber while the barrel was cooling down to shoot, and the velocity picked up over 100 fps. Makes sense as I am sure a hot barrel is way over 100 degrees inside,as it gets hotter than that outside.

You mean you 7x57 didn't have a fast barrel?.. ....The more actual pressure measurements are coming out the more it's being shown that traditional pressure "signs" are unreliable.
I hope that the price of PSI systems and strain guages keeps coming down so that more and more reloaders can test some of their old favorite miracle loads can be shown for what they are. Thanks for the post, I hope lots of guys read it.........DJ

This is proof to me that the old conventional pressure signs are unreliable except as gross indicators of pressure.

I've tended to use heavy bullets in most of my rifles, h0wever I stopped at 2550 FPS with the Hornady 154 gr. Load. Heck, you've been getting the same velocity as the Hornady Light Mag with a 139 gr. bullet. I use the S&B 173 SPCE load quite a bit hunting and only get about 2385 fps out of my 24" barrel. I was looking at the H414 loads and the max I found was about 47.3 grains giving 2635 FPS, you must have been really pushing to get much more than that in the case. Anyway, glad to hear the actual test results, and happier you never had a problem with the load.

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Originally posted by jstevens:
This is proof to me that the old conventional pressure signs are unreliable except as gross indicators of pressure.

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Did you ever measure the case head expansion on new brass?

Case head expansion on this load is less than .001. I think most ran .0007-.0008, it's been a few years since I worked up this load. As I said, this kind of ruins my faith in brass expansion in either case head or expansion ring as an accurate pressure indicator.

In general terms the brass case is part of the gun. Such things have been working now since the mid 19th Century.

That Pressure Trace. It's something glued to the outside of the barrel is it not? How is it calibrated?

Pressure Trace

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I finally ventured out into the cold and fired three shots with a new pressure trace strain gauge system. For years I've used a heavy load of H414 with a 160 grain Nosler as a standard load that goes over 2800 fps. This load has been hunted in 100-degree weather and shows no pressure signs in any of the conventional ways. Case head expansion, cases fall out of the chamber, primers not flat, no bright spots in the extractor area, primer pockets never get loose until 8-9 reloads. Several of the others here use a similar load with H414. I think this load proved right away how inadequate the conventional methods are, as the pressure reading was over 70000 psi on all three shots.

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Originally posted by djpaintles:
You mean you 7x57 didn't have a fast barrel?.. ....The more actual pressure measurements are coming out the more it's being shown that traditional pressure "signs" are unreliable.
I hope that the price of PSI systems and strain guages keeps coming down so that more and more reloaders can test some of their old favorite miracle loads can be shown for what they are. Thanks for the post, I hope lots of guys read it.........DJ

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The only thing we really DON'T know is how much pressure is safe in any given combination of rifle action/cartridge case brass hardness/composition. I once read somewhere that "brass begins flowing at 60,000 to 65,000 PSI, and cases are ruined at these levels due to primer pocket swelling." Now, it seems that in some cases, the primer pockets aren't being ruined these days even at "blue pill" pressures. What IS acceptable? SAAMI doesn't load 8X57mm stuff much over 35,000. But up to 64,000 is acceptable for the 6mm Rem., even though the case is no stronger than an 8X57mm. Of course, we all know WHY the 8mm is downloaded. But my question is, how do we know what IS permissible in a modern strong action like the Ruger No. 1 using a new .270. .280, or .30/'06 case? No amount of actual knowledge of the pressures of a given load is of much use unless we know this!!

Savage 99

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Is the sky falling? Some also warn of metal fatigue.

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Metal Fatigue is a real issue but the trick is that the fatigue is over many many cycles of forces that come close to or actually exceed the yield strength of a metal.

I suppose if one continuously pushed 70,000-80,000 PSI one cauld do that but it's also not for sure that this is the case as we really don't know what some of the metals are in the bolts and actions.

I've been exposed to many hydraulic fatigue failures and can attest to the fact that metal will crack and eventually fail when stressed too much and enough cycles. However it never seems to go BANG.....usually there is a stretching and warnings of impending failure then all hell breaks loose.
In a rifle action I have never seen this and would not be too concerned about it.....possible I guess but I'd think one would encounter serious trouble before the action broke completely.

How is it calibrated?

The chamber is a big hollow spring. When the cartridge goes off, the spring stretches. The properties of steel are well known. If you know the shape of the steel (ID and OD), you can calculate how much the spring stretches per psi. The strain gage directly measures stretch. So if you know the amount of stretch, you know the psi. If you know that, the system is calibrated.

metal fatigue

There is a well accepted rough model that says that if you take the log of applied stress, and the log of number of stresses, and make a graph of the two, the 50% failure rate forms a straight line. The net of this is that failure rates increase exponentially with applied stress.

how much pressure is too much?

Dang good question.

I believe that the correct answer is that SAAMI pressures represent an economical operating point. Experience says that if we are SAAMI or below, unexplained failures are very few, and barrels and cases last acceptably long.

El Deguello
I don't guess I really know what a 7x57 case will hold reliably as far as pressure, so all we can go by is SAAMI specs. I wouldn't be against loading it to the max for a 6mm or 257 Roberts as they obviously use 7x57 brass. The 70000 psi mine registered is too high. My Ruger will handle it, as it's still in one piece and functions fine. I'll still back it off to about 48 grains of H414 and try it then, velocity should drop to a bit over 2700 fps, I'll never know the difference. Another interesting side note is that 48 grains is exactly the Hodgon manual max. listed in a modern Ruger in 7x57 with 154-162 grain bullets at I think 2710 fps.

I used a max load of H414 in my 338-06AI in Namibia this past September. Don't know the exact temps but it was sweltering hot in the north and freezing cold 900 miles farther south. I sighted in both places and hit to point of aim both hot and cold. From my experience then, H414 is temperature insensitive.
I used AA MagPro in my 25-06 and found it was not temp sensitive either.

My Oehler 43PBL does not register psi as absolute. Does the Pressure Trace system read absolute psi?

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Does the Pressure Trace system read absolute psi?

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Yes. If you know the ID and OD of the chamber, and the properties of steel, then you know how much the chamber will stretch for applied pressure. The response of the gage itself to stretch is known. The gain of the amplifier connected to the gage is known. You can then directly relate voltage to PSI.

The alloy of barrel steel can vary as can it's specific properties such as it's hardness. Even if it's annealed to a particular hardness it's done within a range.

Some barrels might be a particular alloy such as 4140 and another might be off spec or stainless steel for that matter. For instance I read that LW barrels are quite hard. This variance in hardness will affect the "stretch" so is this variable and all the others mentioned a input into the program?

Since I don't think that it is I am going back to what Bob Hagel says that every rifle is an individual. Keeping in mind that the brass case is usually the weak link that's where I will continue to focus my primary observations.

Savage99,

What you say is true enough, but the particular thing you need to know about steel is not the hardness. It is the Poisson Ratio. After doing a fair bit of research, the consensus of metallurgists is that this number is "remarkably constant" over a broad variety of steels, and that you can satisfactorily use one number for any steel that is likely to be made into a gun barrel.

Every rifle is an individual. Every rifle also follows the laws of physics. If you follow the appropriate protocols, the results that the strain gage system produces will be correct for the rifle it is measuring.

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Originally posted by jstevens:
Case head expansion on this load is less than .001. I think most ran .0007-.0008, it's been a few years since I worked up this load. As I said, this kind of ruins my faith in brass expansion in either case head or expansion ring as an accurate pressure indicator.

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I think this load proved right away how inadequate the conventional methods are, as the pressure reading was over 70000 psi on all three shots.

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Hey jstevens,

1. How did you Calibrate your HSGS?

2. What makes you believe the HSGS is correct about your cartridges being over 70kpsi?

3. Likewise, then do you believe the CHE reading you got are incorrect?

So as not to give anyone the impression I'm trying to "bait you in", this will be my only post to this thread. Really just curious as to what makes you "think" the HSGS is accurate and the CHE that you measured isn't.

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Originally posted by ASS_CLOWN:
What does Poisson's ratio have to do with stiffness, anyway?

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Originally posted by ASS_CLOWN:
Infosponge,

I commend you on you search engine skills!

Now, in your OWN words, would you mind explaining what those two equations refer to?

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Respectively, radial strain and circumfrential/hoop strain in a cylindrical, thick-walled pressure vessel.

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Please explain what each of the variables are and WHAT they are.

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Please explain what the difference between "what" each of the variables are and "WHAT" they are is.

The Variables

'a' is the inside radius
'b' is the outside radius
'p_a' is the interior pressure
'p_b' is the exterior pressure
'r' is the radial distance from the axis of the pressure vessel

The Constants

'E' is Young's Modulus
'v' [sorry, no nu key on my keyboard] is Poisson's Ratio

Now, of course, in the current discussion, the roles of the variables and constants are reversed, since we are talking about fixing the geometries and pressures while varying the material properties.

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I know precisly what Poisson's ratio is used for, as well as the other TWO ELASTIC CONSTANTS, and how they are all related by Hooke's law.

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Two? I only see one constant other than Poisson's Ratio in the above equations.

Now, if you could provide some additional insight into the magnitude of the strain delta from the variations in Poisson's Ratio and Young's Modulus for the various steels and hardnesses typically used in barrels, I'd appreciate it far more than ad hominem insinuations. I don't have the appropriate data on hand, and from a rough analysis of the basic data I do have on the extremes of material properties in steel, I get a fairly crude estimation of a maximum possible variation of somewhere between about 2900 and 11000 psi resulting from using the most widely different steel types. My intuition is that the variation in material properties of the steels actually used in barrel construction isn't anywhere near that large, and that the resulting strain delta from these material differences is also correspondingly smaller -- but I've no proof of that at this point.

This thread is way, way over my head, but that has never stopped me before:

It seems to me that the standards for pressure are intended to ensure that if several things combine to raise pressure, that it will not rise so high that there is risk of action failure and/or injury, and therefore it is no surprise that loads only slightly in excess of the standard may function perfectly for many years? The surprise comes when these rounds are pressure-tested.

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Originally posted by ASS_CLOWN:

Let see what would be the error if "E" (E=29600000 psi) was off by:

2900 psi - 0.009797%
11000 psi - 0.037162%

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You misunderstand. My crude estimate is that the strain gage measured pressure will vary by somewhere between 2900 and 11000 psi if the pressures and geometries are kept the same while the steel material properties differ by the extremes of the limited data I have available. That is at magnum level pressures (i.e., 65000 psi), so the error (or strain delta) is between about 4.5% and 17%.

BTW, what role do you think the shear modulus of elasticity plays in a thick-walled, cylindrical pressure vessel?

My research was a little simpler.

I found the equations, and, if memory serves correctly, Young's Modulus is a term in the Poisson Ratio. A university professor had researched the numbers, and a quick look at the equations told me that the "remarkably constant" statement was plausible. If memory is correct, the Poisson Ratio can be relatively constant, even though Young's Modulus is different for different hardnesses of steel. So, I had a satisfactory answer, and stopped digging.

If I am wrong, I will again happily throw away and old, incorrect idea.

At any rate, the range of steels used for barrels is fairly small. They don't make them out of railroad rails anymore, except in Pakistan.

In the end, microstrains is probably a more fundamental measure than PSI. With piezo equipment, you can get PSI, and, with basic engineering, design barrels that do not suffer excessive strain as a result of typical pressures. I think the choice of PSI as the unit of measure was possibly just a matter of designing with measurements that you could actually get. In my mind, if microstrains had been available years ago, barrels and bolts would have been designed directly in those units, not PSI.

AC, Info got accused of being a web rat with no technical background. So, I proposed a small test for him, which he gamely answered. A couple of his detractors were notably discomfited by the result. He is quite technically competent, though I think the Schroedinger Wave Equation in three dimensions does give him some difficulty at times, and he has not yet located the center of mass of the universe.

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Originally posted by denton:
My research was a little simpler.

I found the equations, and, if memory serves correctly, Young's Modulus is a term in the Poisson Ratio. Somebody before me had researched the numbers, and a quick look at the equations told me that the "remarkably constant" statement was plausible. If memory is correct, the Poisson Ratio can be relatively constant, even though Young's Modulus is different for different hardnesses of steel.

If I am wrong, I will again happily throw away and old, incorrect idea.

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Well, denton, you're wrong. Young's Modulus and Poisson's Ratio are different things, and they are related by the Generalized Hooke's Law -- exactly as ASS_CLOWN hinted at. Both Young's Modulus and Poisson's Ratio play a role in hoop strain, as their presence in the above equation indicates. With data on Young's Modulus and Poisson's Ratio for the various types and hardnesses of steels used in barrels, it's simple to calculate the difference in strain for the same load pressure in typical barrels constructed from those various types and hardnesses of steel. I don't have those data, so the best I can do is a very crude estimate based on one source's listing for the extrema for different steels. In the extreme, it looks like the difference in material properties is significant, but I don't have a good grasp on the significance of the strain delta for typical barrel steels.

Finally, yes, the three-dimensional Schroedinger Wave Equation does give me troubles, as do Einstein's Field Equations, but I have located the center of mass of the universe -- it's wherever you want it to be, since no one point is privilidged and all work equally well as the center of mass.

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barrel wall thickness will be lucky to within 0.002" at the strain gage position (another 1% to 2% error).

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OD runs around 1.200", and I think you can get that within .001", or .0083%. ID is more difficult, but obtainable to within .002" out of about .450", or about .44%. I think dimensional accuracy is better than you have indicated, expecially if you repeat and average the measurements to average down random noise.

We're not that far apart on our estimate of accuracy. I'll allow plus or minus 2% without a battle, and that is satisfactory. 3% is still quite a good system in this context. Of course, I cut my teeth in the days of slide rules (two significant digits) and analog voltmeters (3% of full scale).

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Well, denton, you're wrong.

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Then I have the great pleasure of discarding a wrong, old idea and replacing with with a better one.

I didn't intend to start a physics discussion, but I do know that if my pressure trace is 6 % off, my highest pressure trace was 74767 psi, so it would still be over 70000 which is 6000 over any SAAMI specs. Case expansion is the same as an old load of 51.5 IMR 4350 with a 140 grain that went 2875 fps.

Ok, I've done a more complete analysis. Still using the most extreme data I have for steel material properties, I figure that the maximum difference that the strain gage system should calculate from assuming constant material properties when firing a 65000 psi load from a 6mm Remington in a 1.2" diameter barrel is about 3360 psi, or about a 5% error. For actual barrel steels it is likely considerably less than this extreme case. If the values that the Pressure Trace uses for Young's Modulus and Poisson's Ratio are in the middle of the range, then the error is about half that of the extreme spread -- i.e., the error resulting from variation in steel properties that the strain gage system would report would be at most 1640 psi.

[corrected a previous arithmetic error]

Infosponge,

What are the exact values of "E" that you are using, and for what alloys?

Hardness doesn't significant effect "E" for any given alloy.

Unless you are considering everything from stainless steels to ductile iron I find your range of "E" to be excessive, or at least it appears to be.

Your equations are not complete for a three dimensional strain analysis, by the way.

ASS_CLOWN

Do the equations not simplify to r, and theta, in cylindrical coordinates?

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I didn't intend to start a physics discussion

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Around here, it is best to have a codeword to indicate "pressure", else this always happens.

A few years ago, I thought that I needed a new hobby to get me out of the house, doing more physically active things. I remembered how much fun I had as a teenager, helping abate the local jackrabbit nuisance. I bought a nice little 223, which, overnight, multiplied in the gun cabinet. Now I spend an hour at the range, and then come home and spend 2 hours analyzing the data. Something has gone horribly wrong.

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Originally posted by ASS_CLOWN:
Infosponge,

What are the exact values of "E" that you are using, and for what alloys?

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28000 kpsi and 30000kpsi. Poisson Ratios of 0.30 and 0.27. The source doesn't specify the alloys, just that this is the range for steels.

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Your equations are not complete for a three dimensional strain analysis, by the way.

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Yes, I know. Plane analysis is about the limit of what I want to tackle.

This chart shows the range of tensile strength of steel vrs hardness. The range over the variable of hardness shows about a 70% change in tensile strength.Hardness/Tensile

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Originally posted by Savage99:
This chart shows the range of tensile strength of steel vrs hardness. The range over the variable of hardness shows about a 70% change in tensile strength.http://www.wmia.org/shopguide/sg2001_ver_hardnesstensile.pdf

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Not relevant. We aren't concerned with tensile strength variation with hardness, but rather with variation in Young's Modulus and Poisson's Ratio with hardness.

Youngs Modulus is the ratio of Stress (what you are interested in to Strain (what you are measuring).
Poissions ratio is the effect on the guage by cross axis strain. eg. If you pull on an eraser
it will get narrower as it getrs longer.
Hardness has no effect on either.
The biggest error is that the stress is not
free of concentrations due to the short cylindrical section over the chamber.
Good Luck1