denton

In following all these discussions i have learned alot and have been wanting to get the pressure trace system for awhile now(before all this discussion).

I am still following the threads to see if Hot Core can come up with an answer on how the SAMMI calibrates their system.

Reading Vaughn's book(awhile ago) he made his own piezo or copper crusher and he had to do the mathematics to calibrate his. Is he an idiot too according to Hot Core?

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Originally posted by denton:

One is that you have no good basis for calculating the bias to correct for a SAAMI cut chamber vs. an average chamber. It is in the 2-3,000 PSI ballpark, but it's still a fairly rough number.

The far more serious problem is that it is only a point estimate.

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Correct.

And those problems are not independent of each other. When taken together, they compound the error in Hot Core's methodology.

Primers can have a significant affect on pressure as well as the variables previously mentioned.

I'm afraid Hot Core will not be able to answer InfoSponge's question.

If one orders two identical test barrels from the same mfg and cuts one chamber with a min spec reamer and the chamber on the other barrel with a max spec reamer, the same round fired in both barrels will not produce the same pressure......one has more volume in the chamber. You could use Hot Core's method to "calibrate" one barrel with the other but one will still always produce higher pressure than the other.....even though Hot Core's method will have them at identical pressures.

Am I wrong Hot Core?

That is the problem. PRE wouldn't show same pressure in checking
min and max chamber with samr brass and load, with same resize die or same measurement factory ammo.PRe with same case, load,
etc, would show more expansion in max chamber with most cartridges,Even though in max chamber pressure would be lower!!!!Now I say most cases as In my 458HE wildcat I used a few Bertram
brass with really hard heads ans long thick corner radius and I
ran 10% plus higher velocities, than the Bell brass which showed
pressure ring expansion at its max loads. Never did get any PR
expansion with Bertram cases.Now where the long radius stopped and transitioned to thin side it expanded, about 3/4 inch up the
case from base.But cases extracted easy.And my math showed we was over 70k psi.So PRE is relative system and to get error
out you have to fit brass to whatever chamber is so as to have min clearance, and max brass support.I had one 458Win die that
made base 8 thousands smaller than 458 listed size so if you used
PRE on that much slop, and my chamber was little large,your results would be screwed up.I honed it out so brass came back to
standard specs, which saved a lot of wearing out brass and made
measuring relative expansion more accurate......Notice I said relative as most factory stuff was little small in base also.
Which is used to get a comparison.
So I used measurments to take loading book loads with right
tolerances(most important) with pressures listed and noted
expansion. If there wasn't any I would go up a little, if there
was too much, back off or try better powder. Ed.

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Originally posted by HogWild:I'm afraid Hot Core will not be able to answer InfoSponge's question.

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Hey HogWild, Just like the last time I "attempted" to discuss this issue directly with you, it appears you still have zero original thoughts or experience to contribute to (what I would much prefer to be a discussion) the argument. And since InfoSponge has gone in the direction of arguing rather than discussing, I will choose to pass.

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You could use Hot Core's method to "calibrate" one barrel

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Wrong again! The actual Calibration Method that can turn a totally useless HSGS into a useful SGS is from JCN(LawnDart) not me.

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...even though Hot Core's method will have them at identical pressures.

Am I wrong Hot Core?

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You are totally correct in believing your concept is completely wrong.

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Any HSGS not Calibrated to the JCN HSGS Calibration Method is as useless to a Reloader as a DEMOCRAT. Of course, once it is properly Calibrated, then it becomes a somewhat useful SGS.

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The very best news for all you folks who are just wanting to argue is, if you do purchase a HSGS and use it without proper Calibration, it should become self-evident about who is right and who is wrong. Use every Pressure Detection Method availabe to you as you Develop Loads and that will keep you from blowing yourself up.

Now, unless I see any posts that choose to discuss rather than argue, I'll just pass on them. Best of luck to all you folks.

Just a FYI, ScottS (or any of his other nick's) is a mechanical engineer, that works extensively with stress/strain and strength of materials.
It's true that he does like to stir the pot, and get people excited now and than, some more than others.

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Originally posted by Hot Core:

And since InfoSponge has gone in the direction of arguing rather than discussing, I will choose to pass.

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Now, unless I see any posts that choose to discuss rather than argue, I'll just pass on them. Best of luck to all you folks.

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It's funny that you ask people to explain positions constantly on posts regarding pressure and then call it arguing when someone asks you.

I'm no genious, but appears to me you are bowing out as you can no longer defend your position. If you are not open to truth......not a bad tactic.......probably minimizes your losses.

I asked a simple question comparing two identical barrels except one has a min spec chamber and the other a max spec chamber. I believe you understood my question exactly but instead of answering the question, you began to question my "original thought" and "experience".

Well, I guess you needed something to say as you don't have an answer to the comparison I made......and you needed some way to bow out......

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From HogWild:I'm afraid Hot Core will not be able to answer InfoSponge's question.

If one orders two identical test barrels from the same mfg and cuts one chamber with a min spec reamer and the chamber on the other barrel with a max spec reamer, the same round fired in both barrels will not produce the same pressure......one has more volume in the chamber. You could use Hot Core's method to "calibrate" one barrel with the other but one will still always produce higher pressure than the other.....even though Hot Core's method will have them at identical pressures.

Am I wrong Hot Core?

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Hey HogWild, Take a minute and look at InfoSponge's last argument prior to your post and then look at your post above. It appears to me that you have simply reworded InfoSponge's post.

Let's however assume that I read that incorrectly and it is an original, non-argumentative question from you. I'll be glad to "discuss" it with you.

So, let's lok at it piece by piece:

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If one orders two identical test barrels from the same mfg and cuts one chamber with a min spec reamer and the chamber on the other barrel with a max spec reamer, the same round fired in both barrels will not produce the same pressure

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What I believe you are saying is:

1. You have two rifles.
2. The barrel dimensions are as close to identical as we can determine by all measurement methods available.
3. You have one SAAMI MAX chamber on one rifle and a SAAMI MIN chamber on the other.
4. "The same round is fired in both barrels."

In number 4 I'm going to go out on a limb and believe you "meant to say" rounds from the same box of factory ammo, or rounds Loaded with the same Load are fired in both barrels.

Then we go to:

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one has more volume in the chamber. You could use Hot Core's method to "calibrate" one barrel with the other but one will still always produce higher pressure than the other

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It is not Hot Core's Method, it is the JCN HSGS Calibration Method. In fact, it is the "ONLY WAY" a HSGS can possibly be Calibrated.

I agree that the Pressures will be different.

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even though Hot Core's method will have them at identical pressures.

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Could you point out where in my posts I gave you that impression. If I did, I agree with you that is incorrect. If I posted something to indicate otherwise, I'll stand corrected and be glad to edit it.

Tell me which post gave you that impression and I'll go back and correct it.

Best of luck to you HogWild.

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In fact, it is the "ONLY WAY" a HSGS can possibly be Calibrated.

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Rubbish.

Last time this came up, I posted quotes and links from NIST showing the correct method. Then CDH posted an example of how he applied the NIST method at work to obtain .02% pressure calibration (non-firearm) without reference to any kind of PSI standard artifact, which doesn't exist anyway.

You aren't doing what meager crumbs of credibility you have left any good by continuing to claim that the NIST standard method doesn't work.

For those who missed it, here are the quotes and links from NIST's (formerly National Bureau of Standards) web site, and CDH's example.

denton, Dec 9, 2004

Quote:
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As mentioned in the page introducing the different uses of process models, the goal of calibration is to quantitatively convert measurements made on one of two measurement scales to the other measurement scale. A process model describing the relationship between the two measurement scales provides the means for conversion. A process model that is constructed primarily for the purpose of calibration is often referred to as a "calibration curve".

http://www.itl.nist.gov/div898/handbook/pmd/section1/pmd133.htm
Engineering Statistics Handbook, 4.1.3.3, Calibration
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So, if you believe that NIST has any authority on the subject of calibration, you have to believe that you can calibrate a system that reads in one type of quantity, based on measurements made in a different type of quantity. The conversion mechanism is a calibration curve. The visual version, is, of course, a graphical curve. The mathematical version is an expression of the form Y = f(x), i.e., the desired output expressed in terms of the obtainable input. That whole section of the book contains extensive discussions on just how to do that.
Quote:
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If the model for the calibration curve is not known from theoretical considerations or experience, it is necessary to identify and validate a model for the calibration curve.

http://www.itl.nist.gov/div898/handbook/mpc/section3/mpc365.htm
Engineering Statistics Handbook, 2.3.6.5. Data analysis and model validation
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In plain language, NIST tells us that if we do not have a theoretical curve, we have to create one empirically. So, do we need an empirical curve? No. We have an established theoretical one. Hooke’s Law is about as well established as any physical principle could be. It tells us that we have an equation of the form Y = mx + b, a straight line. We also have the Hoop Strain Equation, which tells us exactly how to find m and b. There is no need, then, to create an empirical model, because we have a good theoretical model. If we wanted to model current through a resistor, we would not need to go to the trouble of building the model, since E = I x R is already well known, as are the Hoop Strain Equation and Hooke’s Law.

m and b are easily determined using the Hoop Strain Equation and basic electrical relationships, which expresses our Y, pressure, in terms of chamber ID and OD, properties of steel, applied voltage, amplifier gain, etc.

So, there you have it. Strain gage systems are calibrated using standard NIST procedures that do not involve direct comparison to an artifact in the units of interest. That is how commercial piezoelectric systems are calibrated, too, since NIST is unable to supply anyone with cans of PSI to compare with.



CDH, Dec 9, 2004

We do 5 point calibrations on commercial pressure transmitters here in our shop all the time. The setup is basically a calibrated set of weights, a piston, and a compressed nitrogen source. More weights on top of the piston means a higher pressure before the piston rises and begins to vent...and it is a .02% accuracy calibration when we are done with them.

Just one example of an 'indirect' calibration, using mass to calibrate in PSI...we also use a calibrated decade box (resistance source for the not EE/instrumentation types) to do cal curves on RTD based temperature transmitters...

Denton, Dec 9, 2004

Perfect example! You know the area of the piston, the mass, g, etc., and get .02% calibration of PSI without a PSI reference.

I had some original misconceptions about pressure trace system and how it was calibrated. After all, I've used all the old methods of guessing pressure for 30 years or so with some success, if you judge that by the fact that I still have two functioning eyes, hands and my rifles are all still one piece of steel. I just received my pressure trace system, and I think it will be one of the most useful tools I own as far as answering some questions I've had for years. I have it ready to go and as soon as the ice storms are over here, I'm going to put it to use. It should give me some interesting data, especially on some of the less common calibers that I load.

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Originally posted by Hot Core:

I agree that the Pressures will be different.

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But your "calibration" procedure will "correct" the differing pressure readings to be the same. In other words, your "calibration" guarantees an incorrect result in this instance. In fact, if the difference in pressures between the MIN chamber and MAX chamber are greater than twice the error in the pressure value derived from the strain gage using the measurements of ID and OD in the Hoop Strain model, then you have guaranteed that your "calibrated" system is less accurate than it was before you "calibrated" it; and if the pressure differences between MIN chamber and MAX chamber are less than twice the error in the ID-OD/Hoop Strain method, then any improvements in accuracy from your "calibration" are a matter of random chance rather than systematic error reduction.

Makes me wonder what the purpose of your "calibration" is.

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Originally posted by Hot Core:
Hey HogWild, Take a minute and look at InfoSponge's last argument prior to your post and then look at your post above. It appears to me that you have simply reworded InfoSponge's post.

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Agreed, it's the same argument as Infosponge, just tried to simplify as much as possible.

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What I believe you are saying is:

1. You have two rifles.
2. The barrel dimensions are as close to identical as we can determine by all measurement methods available.
3. You have one SAAMI MAX chamber on one rifle and a SAAMI MIN chamber on the other.
4. "The same round is fired in both barrels."

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Very close......and not bad as my post was quick and poorly worded. Let me try your method:

1. You have two test barrels (A & B) from the same mfg (assume each is perfect and identical)

2. A Min spec reamer is used to chamber one barrel (A) and a Max spec reamer is used to chamber the other (B) (same cartridge)

3. The test barrel with the Min spec chamber (A) becomes a test barrel for a powder company and has the best pressure measuring equipment available attached and is SAAMI approved to measure pressure. The other barrel (B) is also used as a test barrel; however, this barrel has a HSGS to measure pressure.

4. Cartridges from the same lot of referance ammo (that should produce 60,000 psi) are fired in each barrel. The average pressure reading from the Min spec barrel (A) is 60,000 psi. The average pressure reading from the HSGS attached to the Max spec barrel (B) is 58,000 psi.

One could "calibrate" the HSGS by adding a correction factor of 2,000 psi to the HSGS reading. (This may or may not be safe) Is 60,000 psi (58,000 + 2,000 psi) the actual pressure produced in the Max spec barrel (B)?

5. The pressure monitoring systems are switched on the 2 barrels. The Max spec barrel (B) still averages 58,000 psi (on the SAAMI approved, best pressure measuring equipment available) and the average pressure reading from the Min spec barrel (A) is 60,000 psi on the HSGS. (Extra Credit: Is the actual pressure in this barrel 60,000 psi + 2,000 psi = 62,000 psi?)

In the above scenario, one has to question what "calibrating" the HSGS did for the accuracy of the HSGS pressure readings. "Calibrating" by this method does not mean you are measuring the actual pressure produced in barrel with the HSGS, it gives you the pressure that would be produced if the same load was fired in the other barrel (the one it was "calibrated" against).

My thought (and admittedly, not that original) is that readings from a "calibrated" HSGS (by the method described above) in the final analysis only let's you know what pressure would be produced if you fired the same load in the test barrel you "calibrate" against ...... and will not be indicative of the pressure generated in the barrel with the HSGS attached. Most folks are wanting to know what pressure is being produced in their rifle.

A few questions:
1. Do you find fault with this logic?
2. What useful info does "calibrating" using the above method (add correction factor to HSGS readings) provide the owner of a HSGS about the pressure produced in his rifle?
3. How does the powder company "calibrate" their approved test barrels?
4. Why is there so much suffering in the world? (OK,.......skip this one)

Hot Core, your last post was polite.....so don't show me up now!

quote:

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Originally posted by HogWild:

My thought (and admittedly, not that original) is that readings from a "calibrated" HSGS (by the method described above) in the final analysis only let's you know what pressure would be produced if you fired the same load in the test barrel you "calibrate" against ...... and will not be indicative of the pressure generated in the barrel with the HSGS attached. Most folks are wanting to know what pressure is being produced in their rifle.

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Bingo!

Of course, what Lawndart wants to know really is what pressure his particular ammo would generate in a SAAMI test barrel -- he just wants to use a strain gage on a non-SAAMI test barrel as a quicker, cheaper, and easier means of getting that information. That is why his calibrating against a SAAMI test configuration makes sense for his purposes. Almost all of the rest of us don't much care what pressure a particular load will generate in some barrel other than our own. What we care about is accurately and precisely measuring the pressure that is generated in our own particular rifle. Hot Core's "calibration" recommendations are not necessary, helpful, or even useful in discovering our particular rifle's pressure. A strain gage employed as denton has described is helpful in discovering that particular pressure within a known and useful range of error.

Hey HogWild, By golly, it is a real pleasure "discussing" the HSGS issue rather than arguing. We may end up agreeing, or we may not, but I most certainly acknowledge your last post as excellent.

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1. Do you find fault with this logic?
2. What useful info does "calibrating" using the above method (add correction factor to HSGS readings) provide the owner of a HSGS about the pressure produced in his rifle?
3. How does the powder company "calibrate" their approved test barrels?

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Let me start with #3 and then go back.

SAAMI has all kinds of Pressure Testing equipment from the old CUP stuff, to the Clerke, to the Strain Gauges and others I can't remember the name of.

Let's consider a single "new" cartridge to simplify things like the 300WSM. Winchester releases the cartridge to specific specifications concerning mechanical dimensions as well as the Average MAX Pressure they intend the ammunition to operate. Multiple barrels are chambered and tested at Winchester using multiple Pressure Detection Devices. Once they have a Load they consider suitable for SAAMI, they send it on to them. SAAMI then runs multiple tests on that "Lot" of ammo to establish a Base Line. This may go back and forth to SAAMI only once or multiple times until Winchester and SAAMI agree on a Load and it is then provided as Calibration Ammunition to other facilities.

If that Procedure has changed over the years, I am unaware of it.

1. For the most part, I totally agree with your logic.

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One could "calibrate" the HSGS by adding a correction factor of 2,000 psi to the HSGS reading. (This may or may not be safe) Is 60,000 psi (58,000 + 2,000 psi) the actual pressure produced in the Max spec barrel (B)?

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Since you should be establishing the initial Calibration with Factory Ammo, it would indeed be bad if that was dangerous in the rifle. I really should have ignored that the first time it came up, because it detracts from the "point" of the discussion.

By your logic, I would agree that the MAX barrel should be adjusted to 60kpsi in "this" example. You are not really increasing the Pressure in the barrel, but simply adjusting the HSGS to read accurately.

There is going to always be some difference from barrel to barrel and chamber to chamber irregardless of how much alike we think they are. (You can easily see this if you have multiple rifles of the same caliber.) But, going back to your question, those differences can be in the barrel, chamber or HSGS. The trick it to get a Base Line Load and know what kind of Pressure it generates in a SAAMI Certified barrel and adjust the HSGS for that difference.

Now you have a useable SGS so you can develop Loads which Average slightly below SAFE MAX and get the optimum results from your rifle/cartridge. (I just short-cut all the fuss and do it with the best Pressure Detection Methods of all time - PRE/CHE. With no Strain Gauges hosing up my firearms. But of course that is also a separate discussion.)

2. Calibrating to a SAAMI Certified Load allows you to know if in fact your HSGS is recording Low Pressure, the correct Pressure, or High Pressure. Just that simple.

Otherwise, you really don't know what Pressure the actual firearm is being subjected to. That is the BIG sticking point I've always objected to with the HSGS, the user just didn't know what he was really subjecting the rifle to.

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Now time for a question for you.

1. A HSGS is attached to a 30-06 rifle of your choice.

2. The SAAMI Average MAX for the 30-06 is 50kpsi

2. A couple of boxes of different types of Factory Ammo with 150gr bullets are shot through the set-up and you get the following Average HSGS readings:
Fed = 51kpsi and 2932fps
Rem = 48kpsi and 3043fps
Win = 50kpsi and 2720fps

(I just pulled them as random Loads from the #26 Hodgdon.)

If you choose not to actually Calibrate to a SAAMI known Standard, which Load would you(HogWild) select to "say" your HSGS was Calibrated by repetitive firings?

Here I go again

Factory ammo cannot be used as a calibration standard.

1. There is NO WAY to KNOW, short of a properly calibrated instrument, whether any ammo (factory or otherwise) will give a higher, equal, or lower pressure in YOUR GUN than a SAMMI test gun.

2.I seriously doubt factory ammo is consistent enough to serve as a proper calibration check, much less a standard.

One cannot use an unknown, inconsistent input to calibrate anything. Sending off ammo to a SAMMI lab would get you into the ballpark, but really only tell you how much difference you would have in your barrel compared to a SAMMI barrel.

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2. A couple of boxes of different types of Factory Ammo with 150gr bullets are shot through the set-up and you get the following Average HSGS readings:
Fed = 51kpsi and 2932fps
Rem = 48kpsi and 3043fps
Win = 50kpsi and 2720fps

(I just pulled them as random Loads from the #26 Hodgdon.)

If you choose not to actually Calibrate to a SAAMI known Standard, which Load would you(HogWild) select to "say" your HSGS was Calibrated by repetitive firings?

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You have confused CUP with PSI. These are not the same thing. 30-06 pressures in the Hodgdon manual are in CUP.

The combinations of pressure and MV's you have posted are impossible. More pressure creates more MV, friction being equal. It's basic physics.

If you use the NIST standard calibration method, instead of trying to invent your own, the problem you raise goes away. If you do you calibration the NIST way, then the pressures you measure are the pressures that that cartridge produces in your rifle.

If you think about it for a minute, what you have done is invent an incorrect calibration method, contrary to NIST. You have then pointed out the problems with your own system, and used the fact that your system doesn't work to try to discredit a system the rest of the world uses, but you don't like. The problems you point out are problems with your corrupt concept of calibration, not with the use of strain gages to measure chamber pressure.

If piezoelectric systems had somehow just recently become available to the masses, you could substitute "piezoelectric" for "strain gage" in all your posts, and still have the same problems you invented for yourself. Yet we all have high confidence that piezo systems work. It's your concept of calibration, not the measurement system, that is the root of your error.

quote:

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Originally posted by denton:


If you think about it for a minute, what you have done is invent an incorrect calibration method, contrary to NIST. You have then pointed out the problems with your own system, and used the fact that your system doesn't work to try to discredit a system the rest of the world uses, but you don't like. The problems you point out are problems with your corrupt concept of calibration, not with the use of strain gages to measure chamber pressure.

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His methods are, however, a good solution to a different problem. If you are interested in manufacturing and selling ammo, then you would like to be certain for liability purposes that the ammo you are producing does not exceed SAAMI maximum pressure when fired in a SAAMI test barrel. An ammunition manufacturer cannot be held responsible for the maximum pressure produced in any conceivable firearm, but he can be and is held responsible for not exceeding specified pressures in the specified SAAMI test barrel. If you want to know to reasonable accuracy and precision what pressure your ammo will produce in a SAAMI test barrel, then you can use either an actual SAAMI test barrel or another, non-SAAMI barrel equipped with a strain gage that has been calibrated as outlined by lawndart and Hot Core to read the same as the SAAMI test barrel. (Or if you are being really persnickety, you can use the quick and easy strain gage setup for most of your work, while only using the full SAAMI test rig for final checks -- as lawndart has proposed doing.)

However, that ammunition manufacturers' problem is simply not the problem most reloaders want to address with a strain gage pressure measurement system. What most reloaders are concerned with is whether firing a particular load will blow up their own particular rifle -- not whether that particular load would blow up a SAAMI test barrel. The point of the exercise for the reloader is to accurately and precisely measure the actual pressure produced in his own rifle -- not to accurately and precisely predict the pressure that would be produced in a SAAMI test barrel. Hot Core's recommendations are not useful in addressing the typical reloader's concern with the actual pressure in that reloader's own rifle. In fact, those recommendations are counterproductive to accurately and precisely measuring that pressure.

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Originally posted by denton:

The combinations of pressure and MV's you have posted are impossible. More pressure creates more MV, friction being equal.

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...and powder, primer, brass, firearm, ambient temperature, atmospheric pressure, yadda, yadda, yadda all being the same. In Hot Core's example, I strongly suspect that at least the powders are not the same.

Calibration to a factory round is a waste of time IMO anyway you look at it. The factory loads to a Max PEAK pressure of SAAMI design. The avg pressure the rounds you are testing will include the round that gives you both max and lowest pressures, The idea that the 10 loads you test will show the true spread of the ammo is optimistic at best, you may find with a strain gage the ammo giving pressures between 64KPSI- 58KPSI with a average of 59500psi. SAAMI says the load gives (or Hodgdon perhaps) 65KPSI what do you calibrate you gage to???

Info...

Powder, primer, brass, temperature, etc. express themselves as input variables to pressure. The only variables needed to calculate MV are pressure as a function of time, and friction, if I remember my Halliday and Resnick correctly. More pressure, or less friction, gets you more MV.

BTW, nice to see you again.

Ol' Joe...

What you have said points out a small problem that SAAMI doesn't address perfectly. According to SAAMI, it's the average peak pressure of several cartridges that matters. Normally, that's good enough. But, what if the SD of the loads is 10,000 PSI (ridiculous example, but just suppose)? You'll have 2.5% of cartridges 20,000 PSI above the mean, and that's dangerous. SAAMI assumes that the SD is 3-4% (I don't remember which) of the mean. Normally, that's good enough, but it isn't a completely rigorous approach. Most handloaders will show less variation than that.

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Originally posted by denton:
Info...

Powder, primer, brass, temperature, etc. express themselves as input variables to pressure. The only variables needed to calculate MV are pressure as a function of time, and friction, if I remember my Halliday and Resnick correctly. More pressure, or less friction, gets you more MV.

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Right, but there's pressure and then there's pressure. The pressure listed in reloading manuals and Hot Core's post is just peak pressure, not pressure as a function of time, so it's not of much use in integrating over time or barrel length. More peak pressure does not necessarily give you a larger pressure integral or more MV, of course.

True. But, if you're working with one bullet weight, in one caliber, which dictates similar powders, peak pressure is very highly correlated with the integral of pressure, since so much of a bullet's energy is imparted near the peak of the curve. But your statement is more strictly correct.

What I should have said is that primer, temperature, brass, etc. are input variables to pressure as a function of time.

quote:

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Originally posted by denton:
True. But, if you're working with one bullet weight, in one caliber, which dictates similar powders...

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Similar powders are dictated only if your goal is similar MVs (e.g., maximum MV while peak pressure remains below a specified level.) In other words, your claim is rather circular. If you don't have the similar velocity constraint, then there is nothing preventing you from, e.g., using a small amount of pistol powder in a large rifle case. That may very well generate peak pressure near the limit while producing MV well below that of a large amount of very slow powder -- even though the peak pressure with the slow powder is less.

Of course, none of that is news to you; I'm just exercising a penchant for correctness in objective discussions .

There is nothing worse than an unexercised penchant. Mine becomes truculent if I don't exercise it.

Of course, you are correct.

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Originally posted by CDH:Factory ammo cannot be used as a calibration standard.

1. There is NO WAY to KNOW, short of a properly calibrated instrument, whether any ammo (factory or otherwise) will give a higher, equal, or lower pressure in YOUR GUN than a SAMMI test gun.

2.I seriously doubt factory ammo is consistent enough to serve as a proper calibration check, much less a standard.

One cannot use an unknown, inconsistent input to calibrate anything. Sending off ammo to a SAMMI lab would get you into the ballpark, but really only tell you how much difference you would have in your barrel compared to a SAMMI barrel.

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Hey CDH, Unless my tea has fermented and got me seeing incorrectly, I do believe we are fairly close to agreeing!

Real glad to see someone besides JCN and myself understand something this "simple".

And yes indeed, knowing the "difference in Pressure" between a specific Load shot in a specific firearm with a HSGS and the same Load(same Lot) compared to a Certified SAAMI Ballistics Lab is the entire point of the JCN HSGS Calibration Method.

Rather than using standard Factory Ammo though, the best way to do the Calibration is by purchasing the actual "SAAMI Calibration Loads". I've just not found access to them unless you have a Ballistics Lab, " BUT " that could have changed with all the folks buying HSGS units. I don't know.

Otherwise, the person with an HSGS really doesn't know if it is wrong-low, correct, or wrong-high.

A Non-Calibrated HSGS = Reloaders Pyrite(aka Fool's Gold)

quote:

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Originally posted by Hot Core:

And yes indeed, knowing the "difference in Pressure" between a specific Load shot in a specific firearm with a HSGS and the same Load(same Lot) _compared to_ a Certified SAAMI Ballistics Lab is the entire point of the _JCN HSGS Calibration Method_.

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And that is because, as I understand him, JCN/lawndart's goal is to test ammo intended for resale. He is not particularly interested (within reason) in exactly what pressure is produced in his strain gage equipped rifle, but only in what pressure the same ammo would produce in a SAAMI test barrel. Once again, that is quite different from the goal of the typical reloader, who wants to know what pressure a particular load is producing in his own firearm. Calibrating a strain gage system so that it reports the pressure that would be produced if the ammo were fired in a SAAMI test rig is not relevant or useful in addressing the typical reloader's concern. It is, in fact, counterproductive.

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the best way to do the Calibration is by purchasing the actual "SAAMI Calibration Loads".

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Only if you believe Hot Core's version of calibration, which NIST and the rest of the educated world do not.

If you actually want to do something like that, the cartridge companies will often give you pressure data, if you give them the lot number of the factory ammo you are shooting. You know that. It was posted a long time ago, by someone who did that. Yet you insist that such an option does not exist.

Once again: You could plug "piezoelectric" into all your posts, instead of "strain gage". The same problems would apply. Do we reject piezo? No. Once you get your head straight on the subject of calibration, and adopt the NIST standard method, all these problems you've invented for yourself go away. In fact, piezo gages are calibrated by the NIST method, too, not by your method.

Hot Core, why do you continue to insist that NIST is wrong, and you are right? What do you think gives you the level of credibility necessary to successfully challenge NIST? The links are there for you to read. NIST's view is unambiguous. CDH's example perfectly illustrates how to do it right. Both are correct, and contrary to your view.

Do you not understand that you are simply dashing your last crumbs of personal credibility against the Gibraltar of measurement standards? To continue saying that you have it right, and NIST has it wrong is foolish and arrogant beyond measure.

You have several times posted the same invented set of numbers for imaginary loads, and asked which load calibrates the gage. You have been repeatedly told that strain gages are not calibrated in this manner, and that your example is irrelevant. If you do the calibration the NIST way, the imaginary problem goes away. Yet you post the same irrelevant example, again and again, imagining that it has somehow proved something. Why?

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Originally posted by Hot Core:

Now time for a question for you.

1. A HSGS is attached to a 30-06 rifle of your choice.

2. The SAAMI Average MAX for the 30-06 is 50kpsi

2. A couple of boxes of different types of Factory Ammo with 150gr bullets are shot through the set-up and you get the following Average HSGS readings:
Fed = 51kpsi and 2932fps
Rem = 48kpsi and 3043fps
Win = 50kpsi and 2720fps

(I just pulled them as random Loads from the #26 Hodgdon.)

If you choose not to actually Calibrate to a SAAMI known Standard, which Load would you(HogWild) select to "say" your HSGS was Calibrated by repetitive firings?

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Interesting you chose examples where less pressure produces more velocity. I'm sure this is possible if one isn't trying to select powders with the optimal burn rate (ex. Blu Dot in a 300 Win Mag) Normally, velocity corelates to pressure fairly well.

Which load would I use to calibrate the HSGS? None of them. I would rely on the accuracy of the strain gage factor (provided by the mfg) and the barrel/chamber measurements for input to the pressure calculation. The accuracy of this system has been tested/verified against SAAMI pressure measuring systems. If it is accurate and repeatable, why the doubt?

I've a few questions about your response to my last post.

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Multiple barrels are chambered and tested at Winchester using multiple Pressure Detection Devices. Once they have a Load they consider suitable for SAAMI, they send it on to them.

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"multiple pressure detection devices" Which of these is the accurate one? How was it calibrated? I think at some point it becomes obvious that a barrel somewhere, sometime was calibrated using the NIST standard calibration method. If it is good for SAAMI test barrels, why not good enough for HSGS?

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The trick it to get a Base Line Load and know what kind of Pressure it generates in a SAAMI Certified barrel and adjust the HSGS for that difference.

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How does this help one know the pressure generated in the barrel with the HSGS attached? Do you think it is impossible to measure pressure in this barrel? Again, (refer to my previous post) it sounded like you agreed with the logic from my previous post. I stated that this informs what pressure a load would produce in the SAAMI test barrel....not the pressure produced in the barrel with the HSGS attached.

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Calibrating to a SAAMI Certified Load allows you to know if in fact your HSGS is recording Low Pressure, the correct Pressure, or High Pressure.

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Well, I have to disagree and I think my last post proves why. We "calibrated" by adding a 2,000 lb adjustment factor (based on comparison to the SAAMI barrel pressures). Adjusting the HSGS reading caused us to go from an accurate measurement to an inaccurate one. The "calibration" made us think we were measuring low......when actually we were right on the money with our pressure measurement. I'm thinking this proves that a scenario does exist where "calibrating" to referance ammo can lead to inaacurate measurements. Agreed?

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Otherwise, you really don't know what Pressure the actual firearm is being subjected to. That is the BIG sticking point I've always objected to with the HSGS, the user just didn't know what he was _really subjecting the rifle to_.

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And after my last comparison, do you see how the pressure reading could be wrong.......even after the adjustment factor is added? Therefore, I contend that one would not know what pressure he is subjecting his rifle to even after it is "calibrated" with referance ammo.

Still think NIST is the way to go.

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Interesting you chose examples where less pressure produces more velocity.

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Hey HogWild, I'd be glad to select other Loads from the Hodgdon Manual and use them as what a person could typically expect as variations from Factory Ammo. But, I see you are convinced(incorrectly in my opinion) the HSGS is bsaically self calibrating:

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I would rely on the accuracy of the strain gage factor (provided by the mfg) and the barrel/chamber measurements for input to the pressure calculation. The accuracy of this system has been tested/verified against SAAMI pressure measuring systems.

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But your next sentence is perhaps even worse.

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If it is accurate and repeatable, why the doubt?

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That is the problem, the HSGS is not necessarily accurate at this point. Until you use a Standard to Calibrate it, you are simply guessing it it correct. It might be, but it also might be providing Low or High information.

As long as you can not grasp the fact that your HSGS out of the box is not Calibrated, then we would just continue in a circle. Let me wish you the best of luck with your non-calibrated HSGS and encourage you to use all other Pressure Detection Methods availabe to you - especially PRE/CHE.

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"multiple pressure detection devices" Which of these is the accurate one? How was it calibrated? I think at some point it becomes obvious that a barrel somewhere, sometime was calibrated using the NIST standard calibration method.

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No, NIST was not around when the initial Factory Ammo Testing started nor when SAAMI was set up as an overseer of Pressure and dimensional Standards.

In the very beginning, it was bad-old Trial and Error that firearms manufacturers established their dimensions and Pressure Specifications around. Not real consistent at all.

Over the years, strides forward were made using old(very old) methods of Pressure Detection. And they did have more variation in those Pressure Systems of old than the ones in use today. But that information was built upon and used as a basis of comparison for the newer systems in place today.

But no, it is certainly not a recent event that they established Pressure Specifications or Pressure Detection Methods. Neither the Factories nor SAAMI are "guessing" about Calibration.

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You either missed some of the posts or your blind faith that Calibration is not needed is skewing your thoughts:

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Hot Core:The trick it to get a Base Line Load and know what kind of Pressure it generates in a SAAMI Certified barrel and adjust the HSGS for that difference.

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How does this help one know the pressure generated in the barrel with the HSGS attached? Do you think it is impossible to measure pressure in this barrel? Again, (refer to my previous post) it sounded like you agreed with the logic from my previous post. I stated that this informs what pressure a load would produce in the SAAMI test barrel....not the pressure produced in the barrel with the HSGS attached.

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Here we were talking about using half a box of Factory Ammo to see what Pressure the HSGS would think it is in that rifle. Then the other half is sent to SAAMI for them to see what the same Ammo from the same Lot does in their Certified Barrel. Once they provide a report to you about the exact Pressure that Ammo provides, then you can determine if your HSGS is reading Low, correct or High.

No I don't think it is impossible to measure pressure in that barrel. But it is impossible to know if the HSGS is providing correct information to you without verifying it to a Standard.

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This next comment from you indicates to me that you simply didn't follow the flow of this discussion, or you really just don't understand what is going on. But, it is apparent in this thread that you are certainly not alone.

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We "calibrated" by adding a 2,000 lb adjustment factor (based on comparison to the SAAMI barrel pressures). Adjusting the HSGS reading caused us to go from an accurate measurement to an inaccurate one. The "calibration" made us think we were measuring low......when actually we were right on the money with our pressure measurement. I'm thinking this proves that a scenario does exist where "calibrating" to referance ammo can lead to inaacurate measurements. Agreed?

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No.

I really don't see any use in going farther. You have overlooked or chosen to ignore most of the thread.(I do that with some of the posters here too.)

Let me just wish you the best of luck and encourage you to use all the Pressure Detection Methods available to you other than the HSGS.

HC, one other thing that has completely been missed by your support of the so called 'JCN calibration' is thus:

A single 'calibration' point is WORTHLESS! There is a very good reason that NIST specifies a 5 point calibration over the FULL RANGE of expected inputs (0%, 25%, 50%, 75%, and 100% of the range of expected inputs). The offset is very rarely linear!

For example: Assuming your theoretical offset of 2000 PSI between a SGS and a SAMMI test barrel with the same ammo for your 30-06, and SAMMI barrel gives 50kPSI, there is a strong reason to believe that the difference at 40k or 60k PSI is NOT 2000! Hence the reason it is called a calibration CURVE...

At best, it is what is known as a (technical term) cal. check, but never a calibration. And don't hammer me for semantics, this is a very critical point if one is to really call something calibrated.

Now, can we just agree that this topic has been really well and truely beaten to death and move on to more productive things, like figuring out why the heck the Astros let Beltran get away, or why I can't get my old .280 to shoot like it used to?

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posted by Hot Core

As long as you can not grasp the fact that your HSGS out of the box is not Calibrated,

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Nobody but you has made the statement that the strain gage system is "self calibrating" or "calibrated out of the box". This is as ridiculous as your claim that the system is calibrated by repetitive firing of ammunition with an unknown pressure. (By the way, which is it? Repetitive firing, or self calibrating?)

How do you expect anyone to take you seriously when you keep inventing stuff like this and your phony EE?

The system is calibrated by measuring the ID and OD of the chamber at the point where the gage is attached, and by entering the factory supplied gage factor. That is in accordance with the NIST standard procedure.

Once you do that, the pressure that the system reads is the pressure that the particular round under test produced in that particular rifle. The silly other problem that you invented with factory rounds producing different pressures in different rifles also goes away.

The fundamental problem is that you do not understand calibration.

The evidence is that if we were talking about piezoelectric pressure systems, all the silly problems you have invented will still be problems. All those problems go away if you just follow the NIST standard calibration procedure.

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Originally posted by Hot Core:

That is the problem, the HSGS is not necessarily accurate at this point. Until you use a Standard to Calibrate it, you are simply guessing it it correct. It might be, but it also might be providing Low or High information.

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No. The strain gage has been calibrated out of the box. At a minimum, identically manufactured gages were subjected to one or more standard strains at the manufacturer, and quality control sampling ensures that the manufactured gages do not slip outside of the specified precision tolerance. That is how the strain gage factor provided by the manufacturer was determined. The gage is calibrated and accurate out of the box within its documented precision.

If that had not been the case, then the proper means of calibrating the gage would be to attach it to material samples that are then subjected to precisely measured standard strains.

Regardless of who correctly determines the gage factor (and, similarly, the precision and accuracy of the electronic amplifier), that factor serves to calibrate the strain gage without any need for SAAMI: the gage factor reflects the rate of change in resistance with change in strain, and the resistance at zero strain (i.e., zero barrel pressure difference between the inside of the chamber and the outside) is easily measured. With the slope of the line and the zero intercept both known to specified precision, the gage is calibrated and accurate to that precision. Unless you think that the physics of Hooke's Law and the Hoop Strain equation for some reason do not apply to your firearms, there is no need to make use of a SAAMI test lab's services to calibrate a strain gage or the measurement of pressure derived therefrom. Other than the documented precision of the gage and amplifier from the manufacturers, the only notable additional source of error in the full pressure measurement system is any misalignment of the gage. With a modicum of care in attaching the gage to the barrel, the resulting error is small, amounting to less than 250 psi at magnum pressure (65 kpsi) for a 5-degree misalignment. Attempting to correct for this small of an error through extensive calibration procedures makes little sense. Using the incorrect procedure of recalibrating the system to read the same as a SAAMI test barrel will almost certainly result in greater measurement errors than those caused by minor gage misalignment.

As long as you can not grasp the fact that a strain gage out of the box is sufficiently calibrated, then we will just continue in a circle. Let me wish you the best of luck with your dangerously imprecise PRE/CHE and encourage you to use all other Pressure Detection Methods availabe to you -- especially strain gages.

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Once they provide a report to you about the exact Pressure that Ammo provides, then you can determine if your HSGS is reading Low, correct or High.

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No. Ammo does not "provide" an exact pressure independent of a particular firearm. All that the SAAMI lab can provide you is a report of the measured pressure that the ammo generates in their test barrel. While that is helpful if your goal is to calibrate your strain gage measurement system so that it indicates the pressures that various loads would produce in a SAAMI test barrel, it is not at all helpful if your goal is to precisely and accurately determine the actual pressures generated by those loads in your particular firearm.

These comments from you indicate to me that you simply didn't follow the flow of this discussion, or you really just don't understand what is going on. But, it is apparent in this thread that you are certainly alone in your propensity to ignore facts and to oppose the seas of reality that you have chosen to attempt to command.

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Originally posted by CDH:

The offset is very rarely linear!

For example: Assuming your theoretical offset of 2000 PSI between a SGS and a SAMMI test barrel with the same ammo for your 30-06, and SAMMI barrel gives 50kPSI, there is a strong reason to believe that the difference at 40k or 60k PSI is NOT 2000!

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In fact, any residual error in the measurement system not accounted for in the gage factor and the amplifier is almost certainly not a simple offset, since it is dominated by gage misalignment. Such misalignment generates a proportional error (essentially equal to the cosine of the misalignment angle), not a simple offset error. However, it is easy to align the gage accurately enough that this proportional error is insignificant for reloading purposes.

One more try:

The barrel of your rifle is a big hollow spring. When you fire a cartridge, the spring stretches outward. You can find out how much force is required to stretch the spring if you know the properties of the material, and its size.

The properties of steel are well known. You can find them in any number of good engineering books.

The dimensions you need are ID and OD. That gives you the thickness of the steel spring.

Once you know the properties of steel, and the thickness of the spring, you can easily calculate how much the spring (barrel) will stretch outward for any amount of pressure you choose to apply internally.

You can set up any number of tools to measure the stretch of the barrel. You can do it with a laser interferometer, you can do it with carefully applied proximity probes, or with piezoelectric transducers. One of the simplest and least expensive ways to measure the stretch is a strain gage.

The strain gage itself comes from the factory with a known response to stretch. The strain gage itself has a known sensitivity, just as a resistor or capacitor has a known value, or an RTD has a known response.

You apply the strain gage, with known characteristics to the steel with known dimensions and characteristics.

You feed the signal from the strain gage to an amplifier with known gain, and view and study the signal. Because everything that is required is known, you know how much pressure is indicated by whatever voltage you see. That conforms fully to the definition of "calibrated".

From ID and OD, then, you have a system that is directly calibrated in pressure.

The system is not "self calibrated", "calibrated out of the box", or "calibrated by repeated firing of ammunition", or any such foolish invention of Hot Core. Those are silly distractions that Hot Core made up.

Hot Core has never come up with any valid reason that the system can't or won't work. Of course, he cannot, because many people are now using the system, and are producing accurate, repeatable results. He simply continues to blindly assert that his is the one and only way to calibrate something, NIST and the rest of the educated world notwithstanding. He thinks that his fabricated example somehow poses some sort of unanswerable question. It does not. It is not even relevant.

Once calibrated, by supplying ID, OD, and gage factor, the number that the system produces is the pressure that your cartridge produced in your rifle, within acceptable limits of error.

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Originally posted by denton:

Once calibrated, by supplying ID, OD, and gage factor, the number that the system produces is the pressure that your cartridge produced in your rifle, within acceptable limits of error.

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Almost. You've also got to take into consideration the pressure that the brass itself supports and any misalignment of the gage. The brass consideration is determined sufficiently accurately and precisely from its material properties and from basic physics equations in much the same manner that the barrel steel is considered. The system software typically compensates for the brass in this manner. Gage misalignment introduces a proportionality constant, but that constant can easily be kept very close to 1 so that it does not introduce significant errors at firearms pressures.

Strictly speaking, the complete strain gage system is not calibrated, but the magnitude of the residual error is known to be small enough that calibrating to correct for some of that error is not necessary. At any rate, calibrating against a SAAMI test barrel is not a useful or appropriate means of decreasing the error in measurement of the actual pressure produced in the non-SAAMI barrel. In order to properly calibrate the complete strain gage system as implemented with a particular firearm, you would need to introduce a known pressure into the bore/brass/chamber. There is no simple way to do that. In particular, firing any type of reference ammo in the firearm will not introduce a known pressure into the system, since it is not known that that the firearm is equivalent to that in which the reference ammo was developed and measured.

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You've also got to take into consideration the pressure that the brass itself supports and any misalignment of the gage.

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True. The brass ends up supplying the constant term in the Y = mX + b type equation, about 4,500-5,000 PSI.

60 minutes on a clock face represent 360 degrees, so one minute on the clock face is 6 degrees. I think I can ordinarily get the gage at least that straight, and cosine 6 degrees is .994... don't think it is a big issue. Besides, I check it to the receiver face with a caliper.

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Strictly speaking, the complete strain gage system is not calibrated, but the magnitude of the residual error is known to be small enough that calibrating to correct for some of that error is not necessary.

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The definition of "calibrated" is that you know that the mean error is small enough to be unimportant to you. If you meet that requirement, the system is calibrated to within an acceptable tolerance. If the conditions you state are met, the system is calibrated.

If you make a distribution of the errors from many measurements, the difference between the mean of the distribution and the true value is the bias. If bias is close enough to zero to suit you, the system is calibrated, or accurate. The standard deviation of the distribution indicates the repeatability of the measurement system. If the standard deviation of the distribution is small enough to suit you, the system is repeatable, or precise.

Ok, accepting that definition of "calibrated", we are in complete agreement on the calibration and usefulness of strain gage systems in measuring chamber pressures in firearms.

That was fun. We were posting at the same time. I added a paragraph on bias and repeatability.