Hot Core, any system that is accurate is calibrated. That's the definition of accurate. So if your PRE system is calibrated, why don't you share with us the PSI numbers some of your favorite loads are producing?

I have tested the system on barrels with a 1.2" OD at the chamber (common) and .9" OD (8mm Mauser). Of course, on the smaller OD barrels, you get more microstrains for the same pressure.

Since I didn't design the system, I don't know exactly what they chose for the bridge amplifier gain. Whatever it is, it is completely determined by one met film resistor, external to the chip, which makes it stable to 50 ppm/degree C or so. The software "knows" the gain, the gage factor, the bridge voltage, etc., and translates it all into PSI.

Well your right, Im trying rebarrel a Garand. The problem is that the opperating rod will most likely break or cause the internals to break before I start seeing any pressure signs from the brass. Thats why Im trying to get a heads up look at the pressures to see if my project will even work.

Denton,

I agree with your regarding S/N ratio and repeatability. Sensitivity related to measured versus actual, too low of a sensitivity and your measured value may be far from the REAL or ACTUAL value. What doesn 500 microstrains equate to in psi?

Also, have you tested pressure on barrels of significantly different tenon diameter, say ultra light hunter and varmint bull barrels? Did you see a difference in microstrains recorded?

ASS_CLOWN

Not really. There was a pressure- predicting slide-rule device sold as part of the Powley Computer set once upon a time. But, it was only good with IMR powders and only gave rough approximations of actual pressures. The only way to know pressures for sure is with a gun that has been set up to actually measure pressures, and since all guns are individuals, pressures produced by a certain combination of brass, powder, bullets and primers in one rifle will give different pressures in the next one. So, basically, the answer to your question is NO!

If I were trying to figure loads for a 6.5mm-06 or 280 pressures to match those of military 30-06 ammo how might I go about doing so? Is there any sort of chart or distribution to look at? Thanks.

There are certain indications in the fired brass.
If your primers are cratering (a raised ring around the firing pin dent) it could be exessive pressure. It could also be that your firing pin is too small for the hole it protrudes from. If the primer is not completely flattened out, the cause is likely the latter.
If there is case head expansion of even as little as .005" that would be exessive pressure. A good dial or digital caliper can tell you that if you remember to measure the case head BEFORE you shoot and then after. Once I have found an accurate barrel, I'd like it to last 5 or 10 thousand rounds rather than burn out in 1000.
If the primer pocket no longer holds the primer in, then you have really overdone it. Likewise, if your extractor is making bright burnnished marks on the case head.
Personally, I will accept some flattening of the primer but any load that completely flattens the primer is too hot for me. I'm not one who thinks that an extra 100fps is the be all and end all of handloading. I spend a lot of time loking for the best accuracy not bullet speed. That is probably why I own only one belted mnag (a 375 H&H in Ruger #1). It IS fun to shoot and is so damned beautiful . . .; besides, its a great way to gather a crowd at the range.
I have seldom found the most accurate load to be at the limits of pressure. Once I have found an accrute barrel, I'd like it to last a few thousand rounds instead of burning out in a 1000 or less.

I have an original, unused Powley PMax pressure guage that I'd be willing to sell/trade. That would be able to answer your question for you, for that particular firearm.

Mark

Hey Dutch, I've explained the PRE and CHE Methods over and over.

Offered to send folks a File all about how " I " do it. And quite a few took me up on it. Most had some minor questions, but it was primarily sharing and discussing results on the "very best Pressure Indication Method in existance".

I just notice you never were interested enough to ask for it, but you were in the Threads where I've discussed how to use it before. So, there is really no need for me to repeat it to you again. If you are really interested, do a search.

As I look at your list, some of those questions have been answered in the past. And some have no relation at all to doing a PRE Comparison Measurement, which means you either weren't paying attention or didn't attempt to understand. Most of them your questions just aren't relevant to the way the PRE/CHE Methods work.

Not interested in playing the game with you, since your desire for answers is not sincere.

I realize it is difficult for you all to justify tossing a lot of money out the window on equipment which can be very misleading and impossible to Calibrate to a known Standard. Must admit though, it is quite funny to watch you all try.

HSGS - Reloaders Pyrite (aka Fool's Gold)

One point is clear; when the case head starts to expand
you are pushing the brass into yield. That is the time to
think over what you are doing.
Good luck!

Well, you could glue a Pressure trace strain gauge to your gun. That setup would run you about $300, if you have the computer.

Second best is to use Quickload interior ballistics software (www.neconos.com), in combination with a chronograph. The Powley calculator is also useful, but much less versatile. However, it is free for the download at: http://www.stickledown.co.uk/

Third best is to use manuals that list load pressures, in combination with a chronograph.

Under field conditions, a chronograph is a pretty darn useful pressure gauge. HTH, Dutch.

Hot Core, you have never EXPLAINED it at all. You have TOLD some of the things you do, and you have ASSERTED that it works. Dutch.

I should know better than to wade into this again, but I guess I am too stubborn!

Denton, HC IS calibrating to a 'known' standard...factory ammo. We all KNOW how accurate that is. Of course, ANY pressure measurement system can be thus calibrated, even the hated HSGS! At worst, the HSGS is a differential measurement, comparing to factory ammo. At best, PRE is the same, with much less sensitivity.

HC, I hate to break it to you, but the 'holy grails' of measurement accuracy are SENSITIVITY and REPEATABILITY! Once a system is set up which gives the same result for the same input, as well as registers measureable changes at suitably small changes in input, you have a good system.

PRE and CHE fail on both counts. I am not saying they are not useful, but they are not the BEST! Many systems have better sensitivity AND better repeatability. Some of them are cheap enough to be usable by the average handloader for less $$ than a new rifle. But don't take my word for it, you are the PRE master. Take 10 pieces of factory ammo and do your CHE measurements. Now reload these 10 pieces 5 times, measureing as you go. Post the results for all of us to analyze. Even more interesting would be to do it with an instrumented rifle, therefore being able to directly compare the 2 results measuring the same event!

HC, I think you just don't trust electronics. No problem there, I am a EE, and I often feel the same. But, just say so if that is how you feel...I swear some of the mechanical engineers I work with would rather they cranked their cars with a handle through the radiatior instead of a battery and starter motor! At least they would then 'understand' how the dang thing worked!

Denton,

I caution you to not mistake repeatability (precision) for accuracy (actual value). I have no doubt that the Strain gage will repeat very well (is very precise), but you have not calibrated the rifle barrel & strain gage system to a series of ACTUAL KNOWN pressures so you do not know the ACTUAL relationship between microstrains and psi.

Remember the definition of Accuracy:

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The ability of a measurement to match the actual value of the quantity being measured

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Remember the definition of Precision (repeatibility):

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The ability of a measurement to be consistently reproduced

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Strain gages are FAR more precise than PRE and I could be lead to believe that your strain gage system is precise (repeatable) to say somwhere between 300 to 600 psi for the vast majority of rifles. As you relatively understand the relationship between microstrains and psi that is.

The accuracy is not there however, as you ONLY have relative calibration, not actual calibration.

Like I said earlier there is a very good reason that the reloading companies give themselves an approxiamtely 5% margin of error with regard to pressure. They don't always do this, but more often than not, their pressure/velocity data shows it.

ASS_CLOWN

It is obvious that you clearly do understand the difference between precision and accuracy. So do I. And you are correct in saying that the strain gage is much more precise than PRE... the actual ratio being about an order of magnitude.



What we haven't agreed on yet is the concept of calibration.



The kindergarten version of calibration is that you compare to an artifact that has a known value of the units you are interested in.



The one and only place you can still do that with primary standards is if you are measuring mass. That is the only primary standard which NIST still keeps in "native" units. ALL OTHER CALIBRATIONS COME BY TRANSLATION FROM OTHER UNITS, EVEN THE OTHER SIX FUNDAMENTAL QUANTITIES OF PHYSICS.



If Y = f(x), and you know x, and f, then you know Y, and can calibrate Y in terms of x. That is the standard NIST procedure, and that is what you do with a strain gage... exactly what NIST prescribes for measuring devices in non-native units.... which is everything but mass.



There are no primary NIST standards for pressure.



There are no primary NIST standards for speed.



There are no primary NIST standards for acceleration.



These are all derived units. You calibrate all of them in terms of other units, Y = f(x1, x2,...xn, k1, k2...kn). If Y is pressure, and I can express pressure as f(microstrains, chamber dimensions, properties of steel, gage factor, bridge resistors, amplifier gain, etc.), and if I can get all the input variables (and I can), I know the output variable to the same accuracy (calibration) as I know the input variables. That is what NIST prescribes, and that is what is done with a strain gage system.



If you follow the procedure, NIST and I think you have an absolute calibration. We could be wrong, though.

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In many cases I doubt it is even that good.  

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It is easily that good.



Thought experiment: You want to calibrate a chronograph. There is no such thing as an FPS standard. You know the distance between the photocells to within .1%, and you know time of flight between them to 10 PPM. How accurately do you know FPS? For all practical purposes, to within .1%.



Same argument applies to the strain gage system. Pressure can be expressed as a function of microstrains, chamber dimensions, gage factor, applied voltage, and amplifier gain. All those input variables are known to better than .5%. You easily know the output variable to a percent or two, and 1,000 PSI is a couple of percent.



SD of the random error for the strain gage system has been measured at 667 PSI. Random error for the PRE method has been measured at 6,800 PSI.



All taken together, 1,000 PSI is a reasonable statement of the strain gage's absolute accuracy. Accuracy = calibration.



What is the absolute accuracy of the piezo system? Little if any better than that.