In some research that I've been doing to figure out a way to better measure the pressure in a chamber. I contacted RSI the people that make or distribute the "Pressure trace system" Used here entirely without their permission or consent
This question was posed to them.

Message: I would like to know how the Pressure trace is capable of measuring pressure with (out) a known reference load? I am under the impression that strain gauges need to be calibrated to a known pressure before they can be relied upon. Is this correct? Thanks Kerry

Straight forward question. Yes???

Answer
Kerry;

There is allot of detail in the documentation.

http://www.shootingsoftware.com/ftp/PTII-Help.pdf

The strain gage does not need to be calibrated. Strain gages come with a gage factor that IS the gage's calibration. We have no control over a users ability to accurately measure their barrel or follow instructions and therefore insist the system be verified against a load of known pressure. The Lyman manual and other sources have PSI data for most calibers and loads.

Factory ammo is normally loaded 5 to 10% under Max pressure for the caliber....using SAAMI/CIP protocols which are often 5 to 7 thousand PSI higher then actual pressures in a production firearm.

So there you have it. they INSIST that it be check against a load of known pressure. And they have no control over the end user being able to accurately measure the barrel. Notice I didn't even ask about being able to measure the barrel or chamber?????

This is exactly what we have been debating here off and on for years.
A HSGS (home/haphazard) strain gauge system MUST BE CALIBRATED AGAINST A KNOWN PRESSURE LOAD. No if's and's or but's about it
The same as with any measuring tool calibration procedure That when you calibrate it you must check it against a known standard that has traceability.
If you are just going to town without verifying your equipment to a known standard YOUR NUMBERS MEAN NOTHING.

kcstott

"This is exactly what we have been debating here off and on for years.
A HSGS (home/haphazard) strain gauge system MUST BE CALIBRATED AGAINST A KNOWN PRESSURE LOAD. No if's and's or but's about it
The same as with any measuring tool calibration procedure That when you calibrate it you must check it against a known standard that has traceability.
If you are just going to town without verifying your equipment to a known standard YOUR NUMBERS MEAN NOTHING."

This is exactly what Dr. Oehler, others and myself have been telling you and Hot Core along with a couple others that must be done. This what is simply called; using "reference ammuntion". Dr. Oehler recommends the same thing be done with the use of the M43. Nothing new or original in thought with RSIs statments. They are simply "industry practice".

I would add that the use of "calibration" is not correct. You can "calibrate" many measuring instruments. A simple micrometer is a good example; close until the jaws touch and then "zero" out the dial. You can not "zero" out a pressure reading strain gauge instrument. What you do is to test "reference" ammuntition. If the reference ammuntion measures 56,100 psi and is supposed to be 57,500 psi then you know you have a 1,400 psi offset "refernce" when measuring the psi of other loads. Hence the name "reference ammuntion. The "offset" amount is most often used but to be correct an offset percentage is actually correct. Thus the pressure measuring device is not actually "calibrated" as such. It is the corrected psi figures that are "calibrated" or "corrected" to be more technically correct.

Thanks for the input. The so called "HSGS" are readily found to be quite accurate when referenced against ammuntion of known pressure. Perhaps Hot Core and others will better understand now.

Larry Gibson

Larry, would you be willing to provide more details about the reference ammunition, such as where you get it, what are it's specifications, and how you used in your HSGS system - hopefully with the actual measurements, etc. Thanks. AIU

You don't calibrate a set of calipers by simply zeroing it. That tell you nothing about how far off the
Proper calibration means checking the calipers against a known standard within the calipers range. i.e. gage blocks.

The problem I have with the HSGS it the "gage factor" being added in.
I don't believe it is as simple as that.
How do we know the reading isn't off because of the way the gauge is set up.
And how accurate does the gage need to be mounted if we are measuring micro-strains.
I know i'm nit picking here but I just don't believe it's that simple

quote:

This is exactly what we have been debating here off and on for years.
A HSGS (home/haphazard) strain gauge system MUST BE CALIBRATED AGAINST A KNOWN PRESSURE LOAD.

This is something that has been brought up before. There is NO KNOWN PRESSURE LOAD out there. You can get a standard for weight or linear measurment such as inches or meters but there is no standard for pressure other then in theory.
Referance ammo is simply ammo build to a computed model and checked at various trusted labs to verify it gives close to the pressures it is expected to with their equipment. (this "equipment" isn`t calibrated to any standard either) The readings from the different labs are averaged and the load is given a "rating" of xxxxx psi.
This ammo is then sent to labs developing ammo or reloading data and their equpiment is "calibrated" to agree with this "average pressure". The difference between the average pressure given by SAAMI to the referance ammo and the reading the labs useing it get on their equipment is used to figure the "off set" for calibrating the useing labs equipment, strain, piezo, CUP, ect. No one knows for sure exactly what the pressure of the load really is and you can be sure it isn`t the same in each labs test bed.

The trait that makes a strain gage popular is it is very consistant in its readings. No matter the actual pressure if you find a rifle gives 58K psi peak with a given load then try another and see then same peak 58K psi you can quite sure the pressures are very similar between the two loads. The slope of the burn may vary -and it will show on the trace- different velocities may be clocked but, the peaks will be with in extreemly close in actual pressures. The old CUP and LUP, or HE or PRE are not near as good at resolving changes psi pressure.

I was just reading through my Saami manual and it says the same thing that reference ammo is tested and averaged at the different labs and saami rates it or certifies it as xxxxxPSI avg.
So even the ammo manufacturers are swaging it to some degree

quote:

Originally posted by Ackley Improved User:
Larry, would you be willing to provide more details about the reference ammunition, such as where you get it, what are it's specifications, and how you used in your HSGS system - hopefully with the actual measurements, etc. Thanks. AIU

AIU

It's not all that complicated. "Reference ammunition" is a specific lot of production ammunition that is known for its consistency. It is most often produced by Federal or Winchester. The current lot of "reference ammunition is a Winchester lot of .308W. That is the most often used cartridge. No there is not a "reference" lot of ammunition for each cartridge. The Current Winchester ammunition is very, very expensive and Both Winchester and Federal, along with Dr. Oehler said that the use of strictly "reference" ammunition is not necessary. The use of an ammunition of known psi is necessary. Federal provided me with the lot #s of several lots of particularly uniform .308W ammunition. I was able to locate several boxes of one lot at the Lacey, WA Cabella's.

The test data that was provided to me from the Federal technician was for lot #21V688 which is Federal's 150 gr PowerShok ammunition. It was tested in their SAAMI Spec 10" twist test barrel under the usual test parameters and at an ambient temperature of 70 degrees. The figures given were offset corrected based on the use of Winchester "reference" ammunition in their conformal piezoelectric transducer device.

The corrected psi was 53,400 with an ES of 4,100 psi for a 10 shot test string. The Federal technician further stated they expect 3-5,000 less psi when the same ammunition is tested in their commercial barreled rifles using a measuring device vary similar to the one I was using. The technician was very careful with not divulging some information for propriety purposes and I'm sure liability reasons. He did say they used a somewhat more expensive model than the one I was using. I got the impression, though he was very careful not to admit to it, that they used a M82 Oehler system.

I tested Federal's Lot #21V688 of .308W 150 gr PowerShok in 3 different rifles with 3 different twists; 10, 12 and 14". The ambient temperature was 46 - 50 degrees with the ammunition having been setting for 3 hours in that temperature range. Obviously the lesser temperature would also result in a slightly lesser pressure.

The 10" twist barrel had 76 rounds through it at the time of the test. It recorded a peak pressure (MAP) of 51,700 psi(M43) with and ES of 3,900 psi(M43).

The 12" twist barrel had 2505 rounds through it at the time of the test. It recorded a MAP of 49,500 psi(M43) with an ES of 7,300 psi(M43).

The 14" twist barrel had 225 rounds through it at the time of the test. It recorded a MAP of 49,600 psi(M43) with an ES of 4,200 psi(M43).

Thus we see that the M43 Oehler gave psi readings that are very consistent with expected industry measurements in commercial barrels. Now to extrapolate the use of that lot of Federal .308W as " reference" ammunition for the 10" twist barrel we would divide the 53,400 psi of Federal's corrected psi by the 51,700 psi(M43) in my 10" twist barrel. That gives us a constant of 1.003. Then if I want to consider a PMAP (Maximum Allowable Peak Pressure) of 65,000 psi as a maximum safe psi level for my reloads we divide 65,000 by the constant of 1.033. That gives us a psi(M43 of 62,900 as a PMAP for that particular barrel. I can then develop loads that do not exceed that PMAP and know that I am not exceeding the pressure limits of the rifle or cartridge.

Note; The PMAP is different than MAP. Please do not confuse them.

I also discussed the use of "reference ammunition with a technician at Winchester. He was quite helpful and explained to me the extreme cost of actual reference ammunition. He also stated that "reference ammunition" was not really used that often. I also gave him the pressure data from a specific lot of Winchester .308W PP ammunition I had tested. He got back with me and said Winchester uses "similar" test equipment as Federal except the Winchester Barrel is a 12" twist. He stated the 50,200 psi(M43) I recorded with the M43 is well within the expected psi parameters of that particular lot in a commercial barrel. He wouldn't give too many facts (liability) but said if I used a correction constant of 1.025 I would be very, very close to the pressures of their conformal piezoelectric transducer. He also said they used a 12" twist as that was the original spec for the .308W. He said pressures were usually higher in faster twist barrels and lower in slower twist barrels, not always but usually.

I have 22 different barrels of 17 different cartridge with stain gauges on them to measure pressure with. I tested 3 - 5+ different factory and/or milsurp loads as "reference" through each of them to establish a base and to give me a constant. using that I can load to a given PMAP in complete safety with new or different components. Using modern or appropriate actions I can also load some cartridges to higher MAP/PMAPs than the cartridges are normally loaded to.

A good example is my 45-400-70 (actually a 45-70) built on a Siamese Mauser. I load Barnes Original 400 gr SPs to 2300 fps at a MAP of 62,700 psi. You can't do that safely with CHE. I know because I've tried. I also load my '06 hunting loads using a 190 Hornady SPBT to 2700 fps with a PMAP close to but not over 65,000 psi for use in my new M70. CHE gave no indication of that psi.

Thus you can readily see with the use, as recommended by the manufactures, "reference" ammunition the M43 is quite reliable in giving psi readings consistent with the industry psi measuring equipment. One just has to know how to do it is all. It is not really complicated. Dr. Oehler ran a comparitive test using an industry standard pressure barrel with 5 different methods of measuring pressure mounted on the same test barrel. Thus each shot was measured by 5 different methods; 2 strain guages attached to a M82 and a M43, 2 conformal transducers and one casemouth transducer. The results of his test are very interesting. I do wish he would publish that test. It would indeed open many minds to the accuracy of strain gauge pressure tests.

However, I guess anyone can easily criticise and second guess something to which he has no first hand knowledge. To those of us who have first hand knowlege of the use of strain gauges to measure cartridge pressures we find it a practical and accurate way, alibiet somewhat expensive, to actually know what the pressures generated are.

Larry Gibson.

Larry, Very well stated.

What I think we need to get away from though is calling the numbers you and everyone else is getting from the HSGS/M43 PSI. as they are by definition not true psi readings. and should not be considered such.
If you called it say a "pressure factor" and as you have shown compared to factory ammo as long as you do not exceed the numbers your factory ammo produces you should be fine in terms of pressure with your reloads.
Is that correct?

Basically what I'm saying is if you had a factory load that gave a number of say 75,000 map and your reload were loaded to say 69,000 you would not be over pressure because the "MAP" was based off of the factory ammo and the number is a reference not a standard in the true sense of the term

quote:

Originally posted by kcstott:
I was just reading through my Saami manual and it says the same thing that reference ammo is tested and averaged at the different labs and saami rates it or certifies it as xxxxxPSI avg.
So even the ammo manufacturers are swaging it to some degree

Ol' Joe summed it up pretty well. The older LUP and CUP only measured peak pressure. The strain gauges and conformal transducers measure the pressure trace (time/pressure curve) also.

Larry Gibson

Well what I meant was the factory is averaging their reading too.

quote:

Originally posted by kcstott:
Well what I meant was the factory is averaging their reading too.

Yes, it is given in XXkpsi, +/- Xkpsi.

All of the SAAMI Calibration(Reference) Ammo has a Variance, which means the Correction Factor is never "exact", but better than guessing at what the HSGS is actually indicating.

quote:

The strain gage does not need to be calibrated. Strain gages come with a gage factor that IS the gage's calibration.

And WRONG as usual. All they get is the Resistance value - which - can be changed due to ham-handed folks installing them incorrectly.

quote:

We have no control over a users ability to accurately measure their barrel or follow instructions and therefore insist the system be verified against a load of known pressure.

They nailed themselves with that admission.

Very few people outside Ballistic Labs can get the proper Calibration Ammo. And the cost would drive them away anyhow.

Any Ammo Manufacturer providing Pressure Data such as XXkpsi, without the +/-Xkpsi data, is simply hoodooing the fool who asked for it.

And as Dr. Oehler said, the Haphazard SGS can be off as much as 8%. Seeing posts from some of the people who have totally wasted money on them, I'd say that is being overly generous and Dangerous at Worst.

There is little doubt in my mind why Dr. Oehler quit sell the HSGSs to the general public.
-----

Nice catch KC, it nailed them.

Once again Hot Core wades into a subject he obviously has no 1st hand knowledge of.


Well what I meant was the factory is averaging their reading too.[/QUOTE]Yes, it is given in XXkpsi, +/- Xkpsi.

All of the SAAMI Calibration(Reference) Ammo has a Variance, which means the Correction Factor is never "exact", but better than guessing at what the HSGS is actually indicating.

Not "exact"....well duh Hot Core! All ammuntion pressures have and ES just as the velocities do. The posted MAPs are most often the average peak preassure. Reference ammuntion will always also have an ES of pressure. Obviously everyone but you understands this and also knows that an "exact" pressure figure is not given, an average pressure figure is given. Your obvious and failed attempt to once again obscure the facts are duly noted.

quote:

The strain gage does not need to be calibrated. Strain gages come with a gage factor that IS the gage's calibration.

And WRONG as usual. All they get is the Resistance value - which - can be changed due to ham-handed folks installing them incorrectly.

Again, Hot Core is the one who is wrong here. The gauges are calibrated to a specific resistance value. That specific resistance value is used in the measurement. That is the "calibration" and Hot Core obviously doesn't just quite "get it".

quote:

We have no control over a users ability to accurately measure their barrel or follow instructions and therefore insist the system be verified against a load of known pressure.

They nailed themselves with that admission.

The verification using reference ammunition verifies the users ability to measure the inside and outside of the barrel correctly and to properly install the strain gauge. If the pressures recorded are outside acceptabel parameters then the user should recheck the measurements and the instalation. It' is as simple as that.

It is really quite easy to accomplish the measurements and the instalation of the strain gauge. The directions are simple and easy to follow. Tis is a non-issue for those who have first hand knowledge. For those who don't Hot Core continues to bring it up. It is not an issue.

Very few people outside Ballistic Labs can get the proper Calibration Ammo. And the cost would drive them away anyhow.

Anyone can purchase the reference ammuntion. Winchester is the current provider. Contact their sales department if you are interested in some. However, Hot Core is correct about one thing, the price is indeed quite extravigant.

Any Ammo Manufacturer providing Pressure Data such as XXkpsi, without the +/-Xkpsi data, is simply hoodooing the fool who asked for it.

Obviously Hot Core failed to read my post. Both Federal and Winchester provided the "+/-Xpsi". I refered to it as the "ES" of the MAP. Who is the "fool" here is obvious.

And as Dr. Oehler said, the Haphazard SGS can be off as much as 8%. Seeing posts from some of the people who have totally wasted money on them, I'd say that is being overly generous and Dangerous at Worst.

Hot Core apparently would have you all believe that there should be an exactness of measurement down to the ounce of pressure. There is not. None of the most sophisticated pressure measuring devices for ammuntion provide that degree of accuracy. Most of the older CUP and LUP are only accurate to 500 psi +/-. The more modern piezo systems are accurate to 100 psi +/- based on what a assumed psi is. The use of "reference ammuntion" and a subsequent offset as discussed previously is the method of "accuracy". Still there are the shot to shot variations (the ES of the MAP) and other vaiences. The 8% figure is the industry standard for the difference between what a particular instrument says and what the "reference ammuntion" pressure is supposed to be. If the offset is wthin the 8% all is well. Easy to understand except for perhaps Hot Core.

There is little doubt in my mind why Dr. Oehler quit sell the HSGSs to the general public.

Hot Core "assume's" here. And obviously the first 3 letters apply as per the old saying. I have discussed with Dr. Oehler why he no longer sells the M43 PBL or the M35P Chronograph. Both are very fine instruments. His reasons have nothing to do with the insinuation Hot Core makes. If anyone wants to know Dr Oehler if a very cordial gentleman who can provide the simple truth.
-----

Nice catch KC, it nailed them.[/QUOTE]

Yes the factories do average their pressure readings and none are "exact" as there is a +/- (ES) to them also. The fact remains that the current means of measuring psi of ammunition using the piezo transducers including strain gauges is the most accurate method anyone has yet devised. It is industry standard around the world. However, Hot Core would like us to believe that CHE is the only reliable method even though it has been disproven numerous times over the last 10-20 years. Hot Core has made his stand and like the good captain he is going down with his ship.

Larry Gibson

Since you aren't shooting the "known load" out of the same chamber/barrel as the load pressure was documented for, it is still a relative measure that must be backed up by observation of brass condition and/or velocity measurements.

It is entirely possible that a reference load could be listed as having a safe, low pressure and still dump primers when fired in your barrel!

quote:

Originally posted by BECoole:
Since you aren't shooting the "known load" out of the same chamber/barrel as the load pressure was documented for, it is still a relative measure that must be backed up by observation of brass condition and/or velocity measurements.

It is entirely possible that a reference load could be listed as having a safe, low pressure and still dump primers when fired in your barrel!

True.
The cavet here though is referance ammo is given a pressure rating from a chamber, throat, and bore that is very tight in tolerance and as close as possible to the allowed min spec figures. Factory bores, and even most aftermarket chambers are quite sloppy by comparison. The pressures in these chamber/bores are are almost always lower then what is recorded in the lab test platform. It is pretty much a given though that pressures will not be the same in ANY case and even the various labs that give a pressure figure to SAAMI do not agree exactly. SAAMI might get a psi rating of 62,500 from one lab and 63,800 from the next then find another lab reports 60K even. This is where they get their average and the extreem spread between the high and low reported pressure is the "variance" as Larry said.

Ol' Joe,
That probably works pretty well for more-or-less standard sporter chambers, but when you get into the world of match chambers, all bets are off.

If you get a load that's fine in say, a NATO 223 (long throated) chamber and shoot it out of a CLE or Kreiger 223 (short-throated) chamber, you could conceivably be dumping primers.

quote:

Originally posted by BECoole:
Ol' Joe,
That probably works pretty well for more-or-less standard sporter chambers, but when you get into the world of match chambers, all bets are off.

If you get a load that's fine in say, a NATO 223 (long throated) chamber and shoot it out of a CLE or Kreiger 223 (short-throated) chamber, you could conceivably be dumping primers.

Very possible. The 223 has a shorter throat spec then a 5.56. These 5.56 throats aren`t SAAMI spec chambers though, nor is the 5.56 NATO a SAAMI cartridge, CIP rules it. Some even claim they are not the same cartridges.
There are benchrest smiths and some othercustom builders that will do min spec chambers, or one to the customers specification. The average (that word again) smith though will use a SAAMI spec reamer and all of the barrel makers follow the spec`s on bore diameter, the max allowed tolerance is where you see variation in them.

What I was getting at with the calibration of the strain gauge is the calibration of the entire system.
Now consider this a Home built system.
You need to account for any extra resistance in the system that you build. Now the M43 may be able to compensate for this. But a home brewed system will not. And since we are measuring micro ohms we need to be darn sure that everything is working properly.
Maybe calibration is the wrong term to use but I need to know to what degree can I trust these readings. What's my tolerance or ES expected to be?

8% on a system this sensitive is really nothing. If it was a perfect world I'd like to see .5% accuracy but We are measuring something here that happens in thousandths of a second I can expect the reading to be much better then that.

quote:

8% on a system this sensitive is really nothing. If it was a perfect world I'd like to see .5% accuracy but We are measuring something here that happens in thousandths of a second I can expect the reading to be much better then that.

'Thousandths of a second' is a long time! We've all got cell phones, digital clocks/watches and of course our PC's - well, how fast do you folks suppose those things operate? We measure our PC's in gigahertz - a gigahertz is one billionth of a second or, one thousand millionths of a second! And 'micro-ohms? Perhaps a tad more than that. Transistors have a gain in the region of hundreds to thousands - each! A few micro-ohms here or there is a breeze to measure - nothing to it. Ever been caught speeding? Radar or laser? The laser trap works by measuring the time it takes for light to reach the target and return to the emitter and then computes the changes in that time! Point is, thousandths of a second is real slow!

quote:

Point is, thousandths of a second is real slow!

That lady you were with last week don`t agree with ya. She though 5 minutes was too fast

I`m not sure on this but, I believe the 0.8% accuracy Mr O was refering to included variation in brass alloy, barrel steel, gage adhesive, tempratures, ect, the whole set-up. It is real but, also something that we have very little control over for the most part, as Ken Oehler admitted. That 0.8% though is a very small amout of err. If I didn`t screw the math it comes to 480 psi in a 60K psi load. SAAMI allows a ES of 10Xs that in a lot of cartridges. I think most can accept that small err...

Ol' Joe, It was not 0.8%, it was a solid 8%. When talking about a 60kpsi amount, he said it can vary 4.8kpsi. You read what Dr. Oehler said in this Link.

However, when the people using the Haphazard SGSs don't have a clue as to what they are doing(as larry), I'd suggest the Variance could be as high as 25%, or 15kpsi when they quote 60kpsi(M43). A classic example of this would be in the totally unbiased Kelbro & onefunz Test. Here the results showed clearly that onefunz was TOTALLY CLUELESS(just as larry) about what was actually going on. And as usual, good-old, never-fail, always-reliable, inexpensive, easy to use, easy to repeat - CHE/PRE showed the info onefunz had was nothing but worthless trash. And I'll toss in a GLOAT!

You can also see where Dr. Oehler said the Variances cause the Haphazard SGSs to be APPROXIMATIONS in this Link. As has been shown in many previous posts, most all of the folks who have the Haphazard SGSs really don't have a clue about how they work, or why they work the way they do. An example would be larry's last rant above.

quote:

Posted by larry:
Obviously Hot Core failed to read my post. Both Federal and Winchester provided the "+/-Xpsi". I refered to it as the "ES" of the MAP. Who is the "fool" here is obvious.

larry is correct that I rarely bother reading his totally worthless and confused posts. No need to since he doesn't know what he is talking about.

I do scan posts an occasionally see where he has erroniously posted a XXkpsi(M43), but have yet to see in mention of it being a sheer guesstimate, based on a non-calibrated Haphazard SGS, nor that the chamber dimensions were all guessed at, nor what Correction Factor was necessary. Since I've seen none of that, it is quite obvious to anyone who actually understands electronics that larry just doesn't understand the problems with the worthless device he wasted his money on.

In a Lab environment, the M43 is a different thing entirely.

As for the rest of larry's rant, I can sum up my reply with

Hot Core continues to demonstrate his ignorance on the subject with his inane accusations that no other than he understands.

Ol' Joe and a couple others make some very good points. The 8% variance is the percentage of all variation and how they affect the pressure. The total affect of those variances is easily seen in the ES of measured pressures over a 10 shot string (the usual standard). With cartridges in the 50-60,000 psi MAP range a maximum ES of 7-8,000 psi is acceptable (that is acceptable or desirable). It is all the variables of chamber, throat and barrel dimensions, ignition, burning rate of the powder, tensile strength of the case, expansion ratio, fit of bullet to throat/barrel, etc. that cause the variation in the pressure for each shot. It is also all of those things that cause the variation of velocity for each shot. If we take the 7-8,000 psi as an acceptable ES for the MAP we see that with a MAP of 60,000 psi the "variance" of an ES of 7,000 psi is 8.6%. An ES of 8,000 psi gives a "variance" of 7.5%.

That's where the 8% figure comes from. The MAP is an average pressure and thus an approximation of the pressure of a given load. That is why the industry also looks strongly at the PMAP (Peak Maximum Allowable Pressure) and the MPLM (Maximum Probable Lot Mean). The psi is most often measured down to the 100s because when dealing with an ES of 7-8,000 psi for a given load the difference between 57,245 psi and 57,283 psi is of little relevance. Hot Core and some others apparently think that industry (those in labs) give exact pressure reading s, they do not. The give readings down to the 100s also and there are acceptable variations of between 2.5% upwards of 6.3% variation allowed between the MAP, PMAP, MPLM and the MPSM (Maximum Probable Sample mean). Also there is the MEV (Maximum Extreme Variation) that is allowable with some ammunition. That allows single cartridges of a lot of ammunition to be as much as 20.6% psi above the MAP. When that happens (a single cartridge giving a high psi of not more than 20.6% of the MAP) the ES gets large. All of which contributes to the 8% “variance” mentioned.

Kcstott apparently assumes there should be much more accuracy of measurement involved but there is not. Simply put; it is the variation of the shot to shot psi that gives us the “variance” and the inability to measure the pressure down to the ounce of a psi’s. BTW, kcstott is also correct in that the calibration of the gauge “is the calibration of the entire system. That is why a specific gauge with a specific resistance (calibration) is used. The M43 does indeed account for actual resistance of the gauge. The gauge resistance is one of the required data entry fields. There also is a preoperational check of the gauge resistance by the M43. If the resistance is not correct the test cannot proceed. I can not speak for any “home made” systems.

CHE on the other hand has no set standards for allowable variation. Without knowing the psi crush factor for each lot of cartridge cases used you have no idea of the pressure range of the load tested. You particularly have no idea of a safety margin. Knowing the crush factor would be the “calibration” of the CHE method and obviously that method is certainly not “calibrated” in any way. That is exactly why it has proven itself to be unreliable. Most do not have a means of measuring pressures. Reloaders should stick with traditional methods of working up loads using load data in manuals as a guide. Reloaders should watch for the traditional pressure signs if loading for higher pressured cartridges in actions that are appropriate. If loading for actions that can not take pressures where high pressure signs are apparent then sticking with loads in manuals is the best bet. Relying on CHE can get you into trouble real fast.

Larry Gibson

Larry
Since I never have measured chamber pressures with any device. I didn't know what to expect as far as accuracy goes. And yes I did expect it to be a little more consistent then that. But it is the nature of the design and when 1/10 of a grain = X,XXX amount of increase in pressure I guess we need to look at things in a lager resolution we need to be more concerned with thousands of psi not hundreds
8% doesn't seem all that bad, hell 10% is 6,500 Psi so that is no bad considering a 65,000 psi load. And if the factory says 20% on one cartridge is good well 8% is damn good
I guess I was trying to measure the distance to the moon with a tenth's mic. It doesn't need to be that close to be safe.

And Again I don't indorse PRE or CHE as i have zero control of the hardness of the brass and I have no clue what the Hardness of the shell case is and how much is has work hardened in it's life time.
I have the Documentation that Hot core refers to but I don't accept it as gospel.

And you answered a question again as the M43 won't allow a measurement if the resistance is off. Great that means that added resistance in the wiring or some other place stops the process.
That is what I was concerned with when I was attempting to build my system with an O scope and gages. If I had a bad solder joint or the wiring caused added resistance It would throw off my reading because my system is a dumb system and it is not looking for out of the ordinary parameters. It just takes what is dumped in and spits out a voltage.
Shit in shit out. so to speak. If the quality of the signal on the input side is no good neither is the output side.
Thanks again For enlightening me

kcstott

Let us remember that "when 1/10 of a grain = X,XXX amount of increase in pressure" that it applies to the average pressure. Given the ES an in crease of 1/10th gr may very well result in 40% +/- of the test pressures of the increased load to actually still be below the average preasure of the previous load. Given small increases the ES pressures will overlap.

Good to see we're talking off the same page. Was an interesting discussion to get us here.

Larry Gibson

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That lady you were with last week ...

I should've been so lucky!

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nor what Correction Factor was necessary. Since I've seen none of that, it is quite obvious to anyone who actually understands electronics that larry just doesn't understand the problems with the worthless device he wasted his money on.

In a Lab environment, the M43 is a different thing entirely.

well theres a contradiction right there.

Worthless piece of equipment??? But yet in a Lab environment it fine?????
Describing something as worthless Means it has NO value ...... To anyone.....
But then you say in a lab environment???
I think you're just pissed and that's forgivable. But For someone that nitpicks every little thing about someones post your sure are calling the kettle black bub.
Hot core we started out on the same page but some where your constant thumbing of your nose at Strain gages has gotten old.
I feel that Larry has done an excellent job of of explaining how he obtained these readings.
And you must understand Not once did he ever claim that those reading are etched in stone. He gave many accounts that they are an average measurement of many shots compiled.
I don't accept his number as accurate in anything other then the rifle they were fired from. This is load development not load development for sale to the general public.
10% tolerance of a 65KPSI load is fine with me.
Once I know what the tolerance is I can work with in it to get the results I need. But not knowing the tolerance is a huge problem. In the world of Statistical analysis it's the big picture that tell the story not the small sample size or single reading.


Larry
Well I guess it all relative and the scale of the measurement needs to be considered when noting the psi numbers (Averages of course)

So My idea now is that To quote PSI reading properly. The readings need to calculated to a 1. Average pressure
And then if you want to do statistical analysis
You can calculate Extreme Spread, Standard Deviation, Maximum Deviation, etc
But over all you are deriving these readings from an average not a single shot and these may or may not be compared to reference ammo for verification purposes.
That's the conclusion I was looking for.
I may just have a go at this myself.
As soon as I buy a new oscilloscope

Larry
One thing though I would like to see is testing of the gauges being mounted off axis slightly to see how much error in mounting you can get away with.
How close to perfect does the gauge need to be mounted and if it's off one degree how much will it affect the reading?

kc
To a first approximation it's a cosine function, ie, not too critical.

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To a first approximation it's a cosine function, ie, not too critical.

Well it takes some time to wrap my head around the concept as I'm a machinist and completely use to working to near exact numbers.

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As it was explained to me many years ago, "I feel sorry for those who think ballistics is an exact science. They just don't understand the problems."

That's putting it mildly
I would reason to guess that the number of variables involved would preclude any chance of a reasonably short equation

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Originally posted by KenOehler:
kc
To a first approximation it's a cosine function, ie, not too critical.

Good to seee you`re still lurkin` Ken. Don`t be afraid to jump in more often

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Good to seee you`re still lurkin` Ken. Don`t be afraid to jump in more often thumb

Thanks for the kindness. Larry's studied this more than most and does a good job explaining the strain gage. I'll continue to lurk.

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Originally posted by KenOehler:
[ Larry's studied this more than most and does a good job explaining the strain gage. ...

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Originally posted by kcstott:
And Again I don't indorse PRE or CHE as i have zero control of the hardness of the brass and I have no clue what the Hardness of the shell case is and how much is has work hardened in it's life time.
I have the Documentation that Hot core refers to but I don't accept it as gospel. ...

Your ability to "Challenge the System" is certainly welcome. Any System which can't stand an Unbiased Test needs to change itself, or be removed from the market. GLOAT

At some point in your life if you decide you want to get the SAFE MAX performance from your rifles and at the same time you do not want to be unnecessarily Trashing Cases, then you can always begin using the never improved upon, always reliable, inexpensive, calibratable and totally repeatable CHE & PRE.

Lets turn the tables then.
There is all this talk about how fallible the HSGS is. And how everything must be just so or it spits out unusable information.
Well I agree with that statement.

But I also see that PRE and CHE can be just as fallible. You are expecting someone to take a tenth's mic and measure the pressure ring on a case. For one a normal Micrometer that reads in the thousandth's of an inch can give erroneous readings if a feel is not developed and the mic should be checked against a known standard for purposes of developing a feel. Now a tenth's mic is another story. Your feel has to be on the ball or your readings could be off as much a half a thousandth of an inch. which is huge in terms of PRE and CHE.
Not every one for one will buy a quality micrometer, and not Everyone will take the time to develop the feel needed to make accurate and repeatable measurements.
I'm not saying that you have promoted PRE and CHE as an easy to use easy to learn system. But you sure have not commented on the problems that can be encountered. And that is just as bad.
It makes PRE and CHE out to be the savior of the reloading community. Which it most certainly is not.

My conclusion is that both systems have their potential for errors. And to say one is more prone then the other is misleading to say the least. Someone that installs a gage on a barrel incorrectly can just as easily use a micrometer as a C clamp. They are both delicate pieces of equipment and not made for everyone to use.
In the end the person using the equipment is the key the equipment ability to put forth good usable information

Hey KC, Evan a (relavitely new to using CHE & PRE) Beginner(Kelbro) was able to use CHE to severely whup the totally worthless "non-calibrated", guessed at dimension, Haphazard SGS(M43), which provided totally misleading info. Kelbro provided Relevant, Useful, Repeatable, Inexpensive to acquire, CHE Data. That is very clear in the above Link. CHE showed clearly the Primer Pockets would be way beyond loose, and that is just what happened. The $$$HIGH$$$ M43 indicated everything was just fine and dandy, but of course, that was TOTALLY WRONG!!! Of course, those of us who really do understand Strain Gauges have said that for many years now. The M43 needs to be used in a Ballistics Lab, not by people who can be tricked easily. But, Marketing Hoodoo is difficult to see through by some folks(insert larry, onefunz, and of course my Hero dunceton and his Pressure Trace bologna).

You mentioned that you have the information I've provided on how to use both CHE & PRE. Perhaps you have forgotten that I recommend two different Methods to using them; one for CHE, and a different style for PRE. If a person uses routine Caliper Usage Methods for both measurements, then the results are not as accurate. The document describes it well, as Kelbro showed in his Unbiased portion of the Test. As much as onefunz tried to skew the results, it was not possible to hide how miserably the Haphazard SGS(M43) FAILED, simply because I'd saved the results to look at off-line. Sure glad I did, because onefunz erased the results when he realized how bad, pitiful and foolish, it made his $$$HUGE$$$(M43) investment look.

If people do not want to use CHE & PRE, it is fine with me as they are only handicapping themselves. Sure they can still go by Primer Pocket Tightness as an excellent Pressure Indicator. Only problem is, they may have inadvertently TRASHED a whole bunch of Cases - just as onefunz did - without realizing it until they "try" to Reload them. Or they can load 3, shoot them, go home and see how tight the Primer Pockets are, and repeat the Range Trips. Seems lke a lot of wasted time to me, but it is not my time, so people should do what they want.

As much as folks want to, they can't use Velocity as a Pressure Indicator, because they can get into the same mess as above without knowing it. Or perhaps, be Loaded so low as to not be taking advantage of the SAFE MAX potential of the Cartridge.

I'm simply providing the Best Pressure Indication Method possible for anyone (even the Beginners) to use. But, people should use whatever Method they want to use - even larry. I'll continue to GLOAT over Kelbro's totally unbiased Data, since it proves what I've said for a long time:

A non-calibrated, guessed at dimension, Haphazard SGS = Reloaders Pyrite (aka Fools Gold)! Just that simple.

Hot Core fails to mention that Kelbro's test was fraught with errors and really proves little. He fails to mention the numerous tests I have conducted, in particular the latest with Winchester white box M193. He also implies "bias" in anyone elses tests. Not so. I have thoroughly tested CHE several times and was not biased towrd the M43 because the first few times I did not have a M43. I really didwant CHE to succeed. The problem is it does no. If your primer pockets or case head does not expand at 65K psi and you put that load into the same make of cases but different lot that will expand at 65K psi then you will have blown primer pockets. possible damage to the firearm and possible damage to yourself. With the first load all you know is that it "appears"to be safe and you assume so. However it really is not.

That is the problem with CHE, it is unreliable and unpredictable. You are far better off simply observing the standard "pressure indicators" as addressed in all reloding manuals. However that only applies to loads that approach "case failure" (that is what CHE or primer pocket expansion really is). If you are loading for an older cartridge with less than "modern pressures" then CHE or primer pocket expansion is totally useless.

However, with a M43 accurately measured and known pressures can be loaded for with any cartridge. Obviously Hot Core is extremely jealous and it shows. Too bad he let's that get in the ay of common sense and modern methods of measuring pressures. CHE is unreiable, it is as plain as that.

Larry Gibson