My Lyman manual gives pressure info on some loads but not all. My Hornady and Nosler manuals don't give individual load pressure info. Is there a manual or other reliable source that gives estimated pressure info for standard loads?

Why would they give "estimated" pressure? And even if they did, how would it differ from the estimated pressures provided by the many handloaders who can apparently guess within 1000 PSI from looking at a fired primer?

When loading manuals list pressure, they normally measure it.

Any pressure data you find is gonna be an estimate, cause it ain't your gun.

How, exactly do you plan to use this estimated pressure data? Published loads should be safe in firearms in good condition provided you work up from the low end, don't substitute components willy-nilly, and don't exceed maximums just because you can open your bolt without a hammer. Within those limitations, the pressure is the pressure and knowing it exactly or estimated is of no particular advantage that I can see, except possibly in regard to case life. What matters is getting sufficient velocity and accuracy for the job at hand and going home with all your digits and eyeballs where they belong and not in a baggie.

Ok, estimated was the wrong word to use. Do you know of any manuals that give pressure measurements for all their loads?

If you use Hodgdon's online manual, you will get pressure data in either CUP or PSI.

http://www.hodgdonreloading.com/

Thanks for the link. Good info.

Lyman is the only one I know of, but I only use the Lyman, Sierra, Hornady, sierra and Nosler manuals.

I would like to see something in manuals stating what average maximum pressure they used to develop their loads. I think Speer does that for some rounds. One could assume the manual authors went by SAAMI standards but in the case of older rounds it would be useful to take them to pressures modern firearms are capable of.

E.g., "Ruger only " .45 Colt loads. Okay, that's nice, how about a blurb stating "these loads developed no more than 30,000 PSI in our pressure testing using the firearm noted in the cartridge notes". Or, these 6.5x55 or 7x57 loads developed no more than 60,000 PSI in our modern Tikka test firearm. If you are using a Model 96 or older pre-WWII firearm stop at these loads which developed no more than 51,000 PSI.

Extra work to be sure but it would certainly help those who want to take full advantage of older rounds in modern firearms without extrapolating blindly. I know you can sort of get there by comparing case capacities of similar rounds - 7mm-08 and 7x57 for instance, and loading to similar velocities, but hard data would certainly play to many a loony's (or loonie's) quantitative heart.



Added: the 6.5x55 is a good example. I have a 1915 M96 Swede and don't even approach max loads listed in the Hornady manual for the 6.5x55 which are much slower than those listed for the .260. But in a modern Tikka I don't see why one couldn't load to similar velocities as the .260 loads are showing.

Thanks, I use their hardbound manual and didn't know that either.

Good post.

43Shooter,

OK, here is some pressure info that might help:

Members of the Sporting Arms and Ammnunition Manufacturers Institute (SAAMI) voluntarily adhere to certain standards in guns and ammo, mostly so all ammo will be safe in all rifles made by members. All the companies mentioned so far are members of SAAMI.

The SAAMI pressure standards include Maximum Average Pressure (MAP). You can find the MAP for most cartridges one the SAAMI website, so you can assume that even though a company doesn't list pressures in it's load data, the MAP won't exceed that pressure. In fact, it's usually less than the MAP, because SAAMI standards also include a stipulation that any single round in the tested string does not exceed the maximum.

Loads vary somewhat in pressure over a string, some more than others, which is usually why the top pressure varies when a company does list it. This is also why a handloader can't assume that just because a load averages 62,000 PSI when the SAAMI MAP is 65,000 that there's 3000 PSI to play with.

Companies using piezo-electronic pressure equipment (the most accurate system presently available) do try to use test barrels with minimum-dimension chambers and bores. This means the typical factory barrel will usually produce less velocity and pressure, because both the chamber and bore are normally larger.

Most companies, however, use strain-gauge equipment to test for pressures, usually using a factory rifle. Strain-gauge equipment isn't as accurate as piezo, but is close if the same barrel is tested with SAAMI "reference ammo." This is factory ammo that's been tested in piezo equipment and produces X amount of pressure. The strain gauge will show a different pressure, but the results are adjusted ("offset") to come up with a close idea of pressure. (Strain gauges indicators do NOT show the actual pressure. In fact they usually show a somewhat lower pressure than piezo equipment, something many people--including a few supposed professionals, don't understand. Without reference ammo strain-gauge results aren't valid, except on a comparative basis: One kind of ammo produces more less pressure than another.)

Testing by SAAMI members is supposed to be done under very controlled temperature and humisity conditions, unlike the average handloader who tests outdoors under whatever conditions are when he goes to the range. This is one of a bunch of reasons results will vary considerably from published data.

One company that does use piezo equipment is Western Powders, the distributor of Accurate and Ramshot brands. Their website often lists piezo pressures with a bullets of the same weight but different brands in a particular cartridge. This can be very useful information.

The seating depth can also make pressure vary with the same load in the same rifle.It can be like adding a grain or more of powder just getting close the lands.So once again,pressure can vary greatly from published data and should only be used as a guide.The manual I really like is the Lee Modern Reloading.It list more powder/bullet combinations than any of my other manuals.A lot of what is listed is copied and pasted from other manuals,so it's like getting a bunch of manuals in one.And most of the velocities run fairly close too.

It still won't tell you anything about the pressures you'll get in your gun.

It is my understanding that if you use the same components that the manual shows and load to the same velocity (allowing for differences in barrel length) that your pressure will be pretty close to what the manual got. Otherwise no one would be able to recommend safe loads or even produce factory ammo that wasn't seriously under loaded for safety.

You won't know what that specific pressure is unless they report it, but can assume it is safe enough in your rifle.

That's why I'd appreciate seeing their pressure figures - either measured per load ala Lyman which is preferable or stating the actual MAP they used.


I see in the Nosler manual for the 6.5x55 they state their loads are safe in modern rifles - they do list some pretty impressive velocities - but then that leaves the milsurp or older rifle owner wondering where to stop in his individual firearm.

A few years ago, Ken Oehler shared a data set with me from one of his experiments. He was interested in my analysis of the data set.

The experiment involved instrumenting a barrel with two piezo transducers and two strain transducers. That allows some insightful analysis that probably isn't duplicated anywhere else.

The important findings are:

1. Data from the piezo system and data from a strain gauge system are equivalent and interchangeable for all practical purposes. The difference between the accuracy of the two comes down to the assumptions you make about the contribution of the brass case to confinement of the gas. In Ken's case, there was about a 2000 PSI difference in that assumption. Accounting for that, piezo data was, for all practical purposes, the same as strain data.

2. If you could make an absolutely perfect pressure measurement system, it would not improve the precision (test-retest error) of the measurement of MAP. The two main sources of variation in the measurement are cartridge to cartridge variation and random error in the measurement system. These two variations do not add linearly. The cartridge to cartridge variation is much greater than the measurement system variation, making the measurement system variation very hard to even detect. If you had a perfect measurement system, you could not make a more repeatable estimate than we now get.

MAP is not the actual upper specification on cartridge pressure. MAP is two standard errors below the actual upper specification, the Maximum Probable Lot Mean. However, the MAP is what we load to, because we are getting our data from a sample, and there is always uncertainty in results derived from samples. Setting the working upper limit down two standard errors provides a safety margin.

Yes, it is true that only The Almighty gets perfect, true information. The rest of us have to put up with estimates. Some of those estimates are good enough to be useful. It's still a measurement. But like all measurements, you have to recognize the limits of the measurement system.

The giant uncontrolled source of error in pressure measurements is that even SAAMI does not control barrel temperature, and barrel temperature is a very strong driver of peak pressure. When I'm doing precision testing, I strap a thermocouple to my barrel, just forward of the receiver, and do all my shots at the same barrel temperature. I also control the temperature of the ammunition. It's helpful to control ambient temperature, because it helps control barrel and ammo temperature, but that's not the temperature that counts.

Just for reference, one of the cartridges I tested, using ordinary components, was such that a 30* F change in barrel temperature produced the same change as a grain of powder. (IIRC, that was a Mosin.)

Finally, a strain gauge system can be calibrated and accurate. You believe your chronograph, don't you? So how was it calibrated? Did somebody whip out a can of NIST traceable FPS? Probably not, because such a thing does not exist. You know the distance between the sensors, and you know the frequency of the crystal clock in the chronograph. You count ticks of the clock, and you have transit time. You also have a formula that connects time and distance to speed, speed=distance/time. So you solve the formula and the speed result is as accurate and calibrated as your distance and time are.

To get accurate, calibrated pressure you need strain, chamber dimensions, and the properties of steel. All those are accurately obtainable to three significant digits, maybe four. Then you need the formula that connects those to pressure, and that's the Hoop Strain Equation. So, just like the chronograph, your measurement is as accurate and calibrated as your input variables.

Good stuff Denton.

Is the modulus of elasticity of the barrel steel really known to 3-4 significant figures without testing a specimen from the lot of steel the specific barrel was made from?

Related to the citation above for online data for Hodgdon's suite of powders:

Every year for the last decade or so Hodgdon has published a pretty complete manual of their loading data. It's updated annually. Generally the online site mirrors the manual, including velocity and pressure data for both suggested starting and max loads. I find working with printed data in the manual easier than the online text, especially when I have 5 or 6 sources of loads to compare for some cartridge. Too, it's a lot easier to scan a whole page of a couple hundred loads in the manual, compared with attempting to do the same with Hodgdon's online format.

The manual is sold out at Amazon and Midway, but it's available at Midsouth, Brownells, Natchez, Grafs, and other online suppliers, with some having it on sale.
--Bob
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.

Denton,

Very interesting info from Ken's data, as well as the barrel-temp results--which I have seen myself in certain experiments.

But the problem with relatively low strain-gauge numbers definitely exists. It was first reported to me by two very experienced professionals in the business. Part of the problem, of course, is that some so-called professionals aren't very experienced.

For several years, one lab for a bullet company consistently reported that "improved" cartridges produced more velocity, at the same pressure, than larger cartridges of the same caliber. According to all the technicians at piezo labs I've discussed this with, they've never seen this in ANY cartridges of different powder capacity: In every instance, larger cartridges have always been capable of more velocity at the same pressure. There obviously isn't any reference ammo for wildcats, so the consistent error resulted from assuming the strain-gauge numbers were correct--and they were far from correct, as piezo testing later proved.

I have run also into chronographs that are not accurate, including some that started out accurate but became unreliable over time. Or at least that's the assumption made from direct comparison of their results with an Oehler 35P, by using both chronographs at the same time to record velocities of the same bullets.

Lot to lot variation of steel (of the same alloy) isn't so much of a problem. There are variations between alloys, though. The stainless alloys commonly used are a little different from the chrome-moly alloys, to the tune of 1,000 PSI or so. Apparently Kreiger uses an alloy that produces more difference than that. But, yeah, published modulus of elasticity data for specific types of steel is carried to three significant digits, and that's enough. You might get to four digits by the route you suggest.

In the end, chasing PSI is chasing the wrong rabbit anyway.

If you know PSI, the properties of steel, and the Hoop Strain Equation, you can design an ID and OD for the chamber that will not produce too much strain when the cartridge fires. Excess strain is what causes steel failure, and designers want to prevent that.

So what you really care about is the number of microstrains that the steel exhibits under stress. PSI is just a back door way to get there. Strain gauges measure strain directly. Why not take the direct route? IIRC, something like 500-550 microstrains, and you're good to go.

Of course you also want to operate below pressure levels that will cause brass to fail. Too bad it is so hard to get the wires to a gauge mounted on the brass case.

John...

I have no doubt that some users have produced erroneous results with strain gauge systems. Air bubbles in the adhesive under the strain gauge are one major possible source of error, for example. It isn't easy to get a perfect application, and air bubbles will give you low readings.

But Ken is a careful experimenter, and his strain and piezo numbers were extremely consistent with each other. The main issue was the offset used for the pressure contained by the brass case. Ken was a little frustrated because he was instructed to use a 7 KPSI offset and nobody could supply him with a satisfactory explanation of where that number came from. IIRC, using the Hoop Strain Equation and the material properties of brass, you get an offset closer to 5 KPSI. If I've got that right, a cartridge that reads 59 KPSI on a piezo setup will read 57 KPSI using the strain gauge approach.

At any rate what really matters is microstrains, not PSI, and gauges measure microstrains directly. If you keep the steel in the nice and easy strain region, it will not fail.

The magnitude of outer-surface hoop strains are trivial to measure with resistive type gauges (strain gauges). 400 to 1000 microstrain levels are a walk in the park for a sound and properly calibrated setup. The chamber is elastically loaded during firing and the outer surface strain gauge measures the resulting elastic deformation (hoop or circumferential typically). That data is easy to collect as long as the DAQ is up to the task.

Assuming the gauge was properly sized, bonded, located correctly (OD and ID measurements are known), and the gauge is truly oriented in the hoop direction, the fun really lies on how to relate the OD measured strain to the chamber pressure. The solid mechanics thick-walled pressure vessel solutions are simple and assume an ideal geometry defined by a constant ID and OD....not always the case when dealing with the chamber region of a firearm. The proper location for the gauge is not always ideal given geometric considerations associated with front ring receiver diameter as compared to the barrel shank diameter, barrel taper, etc. A quick FEA of a thick-walled pressure vessel having geometric discontinuities will quickly reveal that a strain gauge can lie within a stress gradient associated with these less than ideal thick-wall pressure vessels as rifle receivers/barrels often are. Strain gauges, especially 125 and 250 footprints (or larger) work best in uniform stress/strain fields..if they're over a gradient well then they're "averaging" the response underneath.

And then there's the issue of dealing with the cartridge brass contribution....brass having about half the elastic modulus as steel and a significantly lower yield strength. For the most part it is along for the ride (relies on the chamber for constraint) but when we're trying to nail down chamber pressure from a remote measured strain..devil in the details.

Denton,

Very interesting about Ken being given a flat 7 KPSI offset. I dunno how that would even be possible, given all the variables involved.

One of my old high school classmates retired from the computer industry in California a couple of years ago. He's now back in Montana, working on an easier-to-use strain-gauge system for average handloaders. He doesn't plan to include a "PSI" readout, because of all the potential problems. Instead it will provide comparative pressures (essentially "microstrains") so handloaders can compare the results in their rifles to factory ammo. We tested a prototype a few months ago and I should probably see how things are progressing.

Thanks to all for the info.

That's an excellent point. Squirrely things happen if you're too near to the receiver or the end of the barrel. I generally put my gauges a bit away from the receiver for just that reason.



Let me know if there is anything I can do to help. I hope this is a smart phone app. Something I can slip in my pocket would be super cool.

That sounds like a very interesting and useful tool. Please keep us posted.

32_20fan,

The brass is one of the problems the head ballistician from a major company stated was a real problem with strain-gauge pressure systems. The phrase he used, as I recall, was "all the layers" between the powder and the outside of the barrel each contribute minor problems in measurement.

As I'm sure you know, in piezo measurement the case wall itself activates the pressure reading, and the walls of that particular lot of cases are tested in a separate machine before the actual pressure test.

One of the labs I've visited frequently became interested in the difference in transducer location SAAMI and CIP, the European system. They build their own test barrels, so ran some experiments and came to the conclusion that the difference is around 1000 PSI.

denton,

I'll talk to him and find out. The prototype he demonstrated to me had a very simple, hand-size read-out system, rather than having to be plugged into a computer.

One of the problems, of course, is keeping the price down to where more handloaders feel they can afford one!

Steve Faber used to sell a unit like that. It just captured the peak microstrain reading. That's pretty straightforward to do, and can be done quite economically. I think mine is still kicking around somewhere. He did some good work on that product.

For whatever reason, the Faber unit had less precision than the PressureTrace. I think it probably related to circuit board layout and such. There are some tricks to excluding electrical interference, such as using a two layer board, with one surface being used just for ground.

You can get strain gauges for $5 if you shop. Some of those are not sealed, so the user will want to cover them in nail polish. But that's one way to keep cost down.

A good place to start is searching the SAAMi web site, they put out a lot of free info that isn't overreaching and will give you a good starting point.

One such of their pages;

Link

Phil

Good link, thanks.

thank you for sharing. although i may not understand all the technical aspects that you and john are mentioning. discussions like this are great added value to the campfire.

I was a die-hard Piezo person until I watched them done at the same time as strain gauge (Thanks, Dr. Oehler). That gave me much more confidence in the strain gauge system.

Interestingly enough, Piezo transducers are calibrated on a system that uses...a strain gauge.

It's interesting to think about the measurement chain for piezo and for strain gauges....

Peizo: The pressure in the cartridge is converted to force by the surface area of the rod. Force applies stress to a piezo crystal. The stress is converted to strain in the crystal by its physical properties. The strain is converted to charge on two opposing faces of the crystal, by the piezoelectric effect. The charge is converted to voltage by the capacitance of the crystal. The voltage is amplified and converted to PSI by the appropriate conversion formulas.

Strain: The pressure in the cartridge applies stress to the chamber. The physical properties and dimension of the chamber convert the stress to strain. The strain is converted to voltage by Ohm's Law. The voltage is amplified and converted to PSI by the appropriate conversion formulas.

The conversion chain for strain gauges is simpler than the chain for piezo devices.

Denton,
Your measurement chain discussion summarizes a lot. I might add that both systems start the chain inside the case and both see similar problems transferring the actual gas pressure to the chamber walls through the brass case. I regard the two systems as "equivalent", with accuracy ratings of roughly two percent. Those who say that accuracy is significantly better than two percent have probably never played the game of making two or more measurements of the pressure generated by a single shot.

The conformal piezo method adopted by SAAMI has the advantage of a using well defined procedures including calibration of the effects of the specific lot of virgin brass used in the loads. You have no calibration with virgin brass exactly corresponding to your load? You are right back to guessing if the calibration is applicable.

Yes, there is such a thing as reference ammunition. It is a valuable tool. The "assessed value" of a particular lot of reference ammo is the average value of the pressure observed by several labs, using their barrels and transducers previously calibrated using SAAMI defined procedures. The reading from each lab is their best estimate/measurement of the average pressure actually generated by the ammo in their lab. The "assessed value" is the "average of the averages" and represents the average pressure of that ammo when fired in a mythical "average" pressure barrel. The pressure correction obtained through the proper use of reference ammo is often referred to as the "barrel correction", and the corrected number is a better estimate of the pressure that might be seen when the ammo is fired in that imaginary average barrel. Simply using reference ammo is not a valid procedure for transducer calibration. Barrels are not equal, even if they are "identical"; that's why we have reference ammo.

The 7000 psi offset mentioned earlier in this thread was not forced on me. It is just my best guess. The offset for the strain gages is very similar to the offset for the conformal piezo transducers. Over the years I've seen many offsets for different brass. They usually vary between 5000 and 12000 psi, and I've been unable to establish any reliable system of predicting the offset for any specific case. My thinking was that 5000 is probably too low for a typical case and 12000 was too high. I just called it 7000 and tried to not outsmart myself. The guess now has morphed into a scientific fact.

Either the conformal piezo or the strain gage can give comparative or relative values of the pressure. (So can any unit that measures only peak microstrain over the chamber.) When you are looking at comparisons only, the offset really doesn't make a significant difference. You get into trouble when you are working near failure pressure (probably brass or action and not the barrel) and try to compare your estimated pressure to the pressure guaranteed by the gunmaker. I don't know any manufacturer who is willing to guarantee that their guns are "good to XXXX psi", and I'm no longer excited by trying to wring the maximum velocity from my loads.

Back to my cave where I've been neglecting pressure measurements and working to improve first-round hit probability at extreme ranges.

Thanks to everyone who has contributed to this discussion.

I too would like to thank the smart fellas...

I'm glad there are smart people working on this. I'll stick to using their insights, as published in manuals, and load to a point where the powder weight and velocity are reasonably inline with what they publish (factoring in barrel length), and the primer looks 'normal', the bolt opens normally and their are no excessive extractor marks, shiny bolt face, etc. Any user friendly tools to better understand pressure in my rifles would be welcomed!

I knew a lot more about "Traditional Pressure Signs" before I began to conduct Piezo pressure testing, or thought I did.

One day we pressure tested some Proof loads. "Traditional Pressure Signs" would have indicated that the Proof loads were not only safe but could probably be increased a little bit. I went home, that night, and pulled bullets from my favorite 25/06 load (which was above book max).

There is no such thing as a free lunch. You won't get appreciable increases in velocity without corresponding increases in pressure.

Get yourself two chronographs or one that reads velocity twice (the genius of the Oehler 35P). If the two readings agree, you've got confidence in the number.

Load to reasonable velocity and you'll get reasonable results.

My new 25/06 load worked just as well as the hotter load...and was a lot safer.

Been quietly sitting in the back of the classroom enjoying the discussion but you hit on something that I've really taken to heart these last several years.


As I understand it, striving for those last 50-100 fps might cost as much as another 5,000 to 10,000 psi. One might be safely at 60 kpsi and 3050 fps for some particular rifle, trying for 3100 could send you to 70 kpsi - speaking in broad general terms, of course.

I used to try for that last 50 fps, just gotta have it! But then it dawned on me the reverse could be used to advantage. You need give up only 50 or 100 fps and perhaps gain a good 5,000 PSI or more safety margin in the process. The animal won't know it and the trajectory won't be meaningfully affected until ranges get way past my comfort zone, but you will increase safety by a goodly amount. Brass lasts longer, bolts don't suddenly get sticky on a particularly hot day, the barrel steel isn't stressed by a few more microstrains (had to google that to enjoy this thread ) per shot - all kinds of good things come from a slight reduction in speed vs. all the nasty things that can happen striving for that last minor gain.

And if someone really needs those last fps just get a bigger combustion chamber.





"No, son, let's walk down there and **** them all!" makes a lot of sense.

Thanks gentlemen great info.

...and to think company's like Sierra publish loading manuals without any pressure testing equipment at all.

I contacted Nosler and Hornady a few years ago and asked why they did not list pressures. Their answers were on par with Johns comment.

If there is a gap between published pressures and SAAMI MAP far to many handloaders would view that as a green light to exceed published max.

Jim,

Homer Powley's rule with single-based powders was that pressure doubles at twice the rate of velocity.

Thanks, then hopefully the situation isn't quite as diabolical as I had suggested. In my example of 3050 at 60 kpsi, a 50 fps increase works out to around a 1.6% increase, so if I understand you correctly pressure would increase by about 3.2% which would only put it at around 62 kpsi - still safe.

But I seem to recall back in the old days that one way to tell when you were getting close to dangerous territory was a sudden larger increase in incremental velocity with the addition of one more increment of powder, suggesting a sudden incrementally larger increase in pressure. E.g.,
57 grains of powder X = 2800 fps
58 grains = 2850
59 grains = 2900
60 grains = 3010 - whoa, time to stop!

Of course, back in the old says we'd load until the bolt sticks, then back off a grain and call it good so the more accurate pressure measuring techniques today are certainly an improvement.

But even if this allows us to more precisely approach safe but maximum loads - for those that have access to and can use the measuring tools, I still support the philosophy that the safety and other benefits of not trying to firewall loads far exceed any downrange benefits of going after that last 1.6% of velocity.


Anyway, as others have already said, it is definitely a privilege just to sit back and soak in the knowledge imparted here by men like Dr. Oehler and Denton and yourself, so thanks to you all for that.