Just ordered my RSI pressuretrace...

will be nice to KNOW what is my pressures, rather than guess at primers!!

will let ya know
jeffe

You'll get a lot of use and enjoyment out of it.

It's quite surprising what you learn by using the PT.

hey, i'd be interested to hear how you guys calibrated your pressure trace. i.e. the data for the "correction factor"

I bought some factory ammo (Hornady) called them with the LOT # they told me the AVG pressure that lot # put out ,45,100-45,600 is what they told me for the 480 Ruger load 325 XTP
,ran it through the PT and put in correction factor.

Sean

quote:

Originally posted by taliv:
hey, i'd be interested to hear how you guys calibrated your pressure trace. i.e. the data for the "correction factor"

Taliv,
i am not searching "52,532.1 psi"... in fact, 52,000 would be amazing... and 50,000-to 53,000 would be great...

Like a caliber (who actually takes a plug gage and calibrates it every time?) or a cheap chrony... anything CONSISTANT is better than nothing.

jeffe

You'll likely get some suprises, I had one on a hot 7x57 load I'd used for years everywhere with no pressure signs. The pressure was 70000 psi, makes you reconsider some or your loads.

jeffe, i understand. my concern is that i did something like installed the gauge wrong and am getting bogus numbers.

I've only had time to put about 15 rounds of 308 through it, but so far, none of them have been above 28k PSI.

I'll do what Sean suggested, I think.

thanks for the info.

If you're getting 28 KPSI readings from a 308, something is seriously wrong, and won't be corrected with the correction factor, unless you're shooting 10 grains of pistol powder.

You may have an air bubble under the gage, or transposed some numbers when entering the dimensions or gage factor, or may have damaged your strain gage in getting it applied.

If you're getting a lot of trace triggering when no shots are fired, you probably bent the gage too sharply right where the little solder pads join the gage grid. That will break the metal, and you end up with an intermittent joint. That will cause the symptom you see.

Those things do happen, which is why RSI is so insistent that you check out the system with a reference load.

You might get a lot of help by contacting RSI.

Hope that helps.

I am with Denton. Either you have a gross input error in your dimensions, or you have not got the gage glued on right. Welcome to the wonderful world of strain gages. By the way, Sean is describing a 'sensitivity' adjustment. Sensitivity is VERY important with regard to getting the right (more accurately stated more right) answer.

ASS_CLOWN

How do you guys calibrate these strain gages for measuring chamber pressures in individual guns?

You calibrate them the same way you calibrate a speedometer, per NIST procedures.

To calibrate a speedometer, you drive a known distance, and time your trip. Divide distance by time, and you know speed as accurately as you know distance and time. There is no artifact with which you can directly compare.

The barrel of your gun is a very stiff spring. As it is subjected to internal pressure, it swells very repeatably and very predictably. All you need is the ID and the OD of the chamber at the point where the gage is attached, the properties of steel, and the thickness of the brass case.

There was a long discussion here a while back about whether steel properties vary enough from type to type to make any difference. The manufacturer says that there is not.

Anyway, you just enter ID, OD, and case thickness. The strain gage measures the expansion, and that is directly relatable to internal pressure. RSI pretty much forces you to do a "sanity check" by firing some fairly well known ammo, just to see that everything is hooked up and working.

I had mine give some low readings, 9-10000 psi on a couple of loads. The only thing I did different was fasten the velcro strap around the cable to keep it from moving under recoil, the pressure readings came back to normal. Could it have been losing contact?

quote:

Originally posted by Ackley Improved User:
How do you guys calibrate these strain gages for measuring chamber pressures in individual guns?

You got them!

Unless they use the "JCN Calibration Method" they are simply fooling themselves into thinking they are Calibrated.

28kpsi from a 308Win! Speaks volumes and volumes and volumes about how well the HSGSs work when they are not Calibrated to a known Standard.

A HSGS (which is not Calibrated by the JCN Method) = Reloaders Pyrite (aka Fools Gold)

It is difficult for me to believe that all barrels are of the same elasticity, especially one chambered for .223 vs. 30-06 vs. 300 WM vs 300 RUM - cartridges that all have different diameters and, hence, surrounded by different steel thickness and producing different internal forces, even given identical pressures (remember Force = pressure X area).

It seems that the only "reliable" way to calibrate your strain gauges is to fire rounds of known pressure - that is, at low and high values bracketing the pressure region of interest. Then extrapolate to the pressure of the unknown.

But, how would you do that? I have two 280 AIs, both built by the same gunsmith with the same reamer - but of course, with different barrels. Given the same reload with the same bullet, same powder charge, and same lot of powder, I get very different results - clearly the same ammo can produce very different pressures in different guns. In this case at leastt 5,000 psi different.

With all due respect, are you sure you're doing the right thing?

The elasticity of a rifle chamber of modern
steel is determined by thickness of barrel and
case and inside diameter of case.In the area where you are measuring the strain with the gauge pad.So that is measurements you put into the system, so the pressure
trace system can work
with that particular combination of case and
barrel size.

When jeffe gets a few readings and the testing going along with chrono readings, I want see if
actual matches my method for big bores..Ed.

Hot Core, you're the one who's "got". You just have Alzheimer's. We went through all this more than once before, and your silly notions of calibration got thoroughly trounced, again and again, by many people. I can't believe you would make such a discredited statement again. Most people would learn, after just one such episode.

NIST is the country's expert on the subject of calibration. According to them, if you can write an equation that relates the thing you are interested in, and want to know, in terms of things you do know, then you know what your interested in to the same precision as your equation and the variables that make it up.

If it were not so, you could not calibrate a speedometer, which is calibrated by equation, speed = distance/time, not by direct comparison to an artifact.

The equations in the case of a strain gage measurement system are the Hoop Strain Equation, and Hooke's Law, both well established and understood. The physical constant required for the calculation is the Poisson Ratio, which is very constant from steel type to steel type, and even more constant within the types of steel used for firearms. As mentioned, the manufacturer researched this, and found the error due to variation in the Poisson ratio to be negligibly small.

If you supply ID and OD at the point that the gage is attached, and case thickness, you have supplied everything needed for the calculations.

Is it perfect? No. But then, neither are the systems used by commercial labs. The same lab, using the same batch of ammunition, is lucky to repeat a 10-shot average within 1,000 PSI. And you can just look at the reloading manuals and witness the lab-to-lab variation.

Is it good enough for practical purposes? Absolutely. It is also about as repeatable as commercial systems, and about an order of magnitude more repeatable than the PRE and CHE methods. How do I know? I ran the measurements, and made the calculations. All the methods are posted for anyone to read and to question.

http://www.shootingsoftware.com/tech.htm

If you don't believe NIST on calibration, you can always go buy several commercial brands of ammunition, and keep your reloads below the hottest brand you can find. The results are quite boring, since they routinely confirm the accuracy of the PressureTrace.

I just love having these discussions come up. Every time they do, more people read about the RSI system, and buy the PressureTrace. Over the past year, I've had correspondence with about a dozen people who have bought the system because of what has been discussed here. That's just the ones I know about.

just FYI, I realize I'm nowhere close to hot on these loads, and I have no plans to get close. 42.0 grains of R15 for a sierra 168g BTHP MK is giving me 2550 fps, which is quite slow, really.

I put 10 rnds of this load and 5 of another through the PT, and the shape of the graph recorded is perfect on every one. According to PT, all of the peaks are within about 2000 PSI of each other.

This lead me to believe that the gauge was reading well RELATIVELY, if not installed completely correclty, but either my measurements of ID or OD or the brass were off, or the correction factor is really a lot more important than I suspected.

I am getting no trace triggering when no shots are fired. In that respect, it's working perfectly. It has never taken a trace w/o a shot, or failed to take a trace with a shot.

I will contact RSI, but you guys think this magnitude of error is still uncorrectable with the correction factor and reference ammo?


to be honest, I'm not quite convinced on the calibration part. Specifically, let's say I call hornady and get their info for my lot. How much variance am I going to see in that pressure due to my gun being slightly different dimensions? It seems like, (as RSI repeatedly stresses) with such precise measurements being so critical, that my gun's chamber could easily be that much different.

i.e. if my chamber is 0.001 smaller than hornady's then would the same load, in theory, generate more pressure in my chamber?

thanks for your help guys and sorry if I started some sort of religious debate here. I'm not interested in that too much; just looking for insight on getting the most out of my new toy.

taliv...

An error of .001" in either the ID or OD is practically inconsequential.

If you're not getting stray triggering, your gage is probably intact. I've busted a couple of them, and have learned to recognize that symptom.

When you simplify the equation for pressure, it is in the form Y = mX + b. The brass case wall thickness is about .019", and it generates the b term, which is usually around 4700 PSI... not enormously important, unless you slipped a decimal.

The "correction factor" is for making small adjustments, not big ones.

So I've worked through my troubleshooting list, and I'm stumped. The folks at RSI know a lot about this, so I think they are your logical source.

quote:

If you're not getting stray triggering, your gage is probably intact. I've busted a couple of them, and have learned to recognize that symptom

Denton I`m glad to see I`m not the only one that`s done this, I just replaced a gage tonight that I damaged the connection at the gage on as you discribed earlier on my first attempt to use it. I e-mailed RSI and recieved excellent support. Now if I can get the weather to cooperate the next day I get off maybe I`ll see where I`m at with this 6.5x284 I`m playing with...

quote:

I bought some factory ammo (Hornady) called them with the LOT # they told me the AVG pressure that lot # put out ,45,100-45,600 is what they told me for the 480 Ruger load 325 XTP,ran it through the PT and put in correction factor. Sean

Hey Sean, I had to get off the computer due to a storm ripping through, or I would have entered this the same time as my last post.

Your "Method" of locating a "Known Standard", running the ammo through your rifle and then "Adjusting" the device for the difference(aka Calibrating to a Known Standard) is the way EVERYONE should be Calibrating their HSGSs. Once a person has done as you did, the totally worthless HSGS now becomes a very useful SGS.

Of course you still have the wires to trip over, bedding problems and hideous appearance to deal with. But, you do have a viable SGS.
---

As usual, anyone thinking you can "Calibrate" a HSGS to an Unknown by repetitive firing is simply full of beans. Just as Taliv has shown, firing multiple shots with Unknown Pressure Level ammo doesn't help you a bit.

As an example, let's say instead of 28kpsi Taliv(or anyone else) had gotten 44-46kpsi with the exact same set-up. Repetitive firing of the same Unknown Pressure Level Loads (as some fools will suggest as doing) convince him the HSGS must be correct and he just got a "Slow Lot" of ammo.

He looks in his various Reloading Manuals and notices SAAMI lists 52kpsi as the operating level for the 308Win. Now is where the problem can arise. Some people would mistakenly believe they can just keep dumping in powder until their HSGS says the cartridge is running 52kpsi as an average. They notice the Velocity is high(don't all HSGS users have a chronograpy too???), the bolt lift is stiff and primer pockets loosen after 2-3 reloads.

I can easily see how this person would think, "Huuumm, signs of High Pressure. Must be a bad lot of Cases!!!"

WRONG-O!
---

So, if you are determined to have a HSGS, let me STRONGLY ENCOURAGE you to ignore the fools who say Calibration can be done with an Unknown - it can't. Use either the method Sean is using or the JCN Method. Granted, Sean's Method is about $350 cheaper.

Speaks very well for Hornady to provide the "Known Pressure Information" for that Lot to Sean.
---

Woooops, nearly forgot:

A HSGS (not Calibrated to a Known Standard) = Reloaders Pyrite (aka Fools Gold)

Hot Core, nobody but you has suggested that a strain gage system can be calibrated by repetitive firing of unknown ammunition.

Why you continue to fabricate such nonesense is beyond me.

You have been given the applicable information from the NIST web site, and continue to contradict NIST on calibration. You have been shown direct quotes from Ken Waters, who popularized PRE, and continue to contradict those. You contradict OKShooter, a professional ballistician, you contradict Ken Howell, and disparagingly refer to him as "Howl", you were given an opportunity to participate in a rigorous test of PRE and strain gages, declined, and now contradict the results of the test. You even contradict yourself, over and over again.

You never produce any data to support any of your unfounded assertions, and you claim to be an EE but cannot answer simple questions that any EE can.

Are you so dense as to suppose that you can get away with that kind of nonesense?

Sigh...

HC, knowing the pressure of a load fired in a different gun and applying that data to a round fired in my gun is like you telling me what the speedometer in your car is saying at 3PM yesterday, and me using that data to 'calibrate' my speedo today at 4PM, when we are not even on the same highway.

It may let you know if you are in the 'ballpark', but it is not a calibration in any sense of the word. 'Sanity check' would be the closest description...and I would wager good money that 3-5kPSI is a common variance between a SAMMI pressure gun used by ammo makers and a OTS factory rifle.

Simple, reasonably accurate measurements setting up a SGS will get one closer than that...so 'adjusting' will only add another variable. More variables, more uncertainty, more potential for error.

Your favored JCN 'calibration' isn't a calibration. Neither is shooting factory ammo. It is at best a sanity check and I feel you are misleading people into doing unsafe things (inputting adjustments based on this method) with your recommendations.

quote:

Originally posted by jeffeosso:
Just ordered my RSI pressuretrace...

will be nice to KNOW what is my pressures, rather than guess at primers!!

will let ya know
jeffe

I'm going to get me one when I grow up.

Be nice if you could run it on a CE device, PDA as opposed to lugging a notebook.

quote:

Be nice if you could run it on a CE device, PDA as opposed to lugging a notebook.

I vote for that!!. Pop your traces up on an IPAQ... that would be just too kewl.

quote:

Originally posted by CDH:
Sigh...

HC, knowing the pressure of a load fired in a different gun and applying that data to a round fired in my gun is like you telling me what the speedometer in your car is saying at 3PM yesterday, and me using that data to 'calibrate' my speedo today at 4PM, when we are not even on the same highway.

It may let you know if you are in the 'ballpark', but it is not a calibration in any sense of the word. 'Sanity check' would be the closest description...and I would wager good money that 3-5kPSI is a common variance between a SAMMI pressure gun used by ammo makers and a OTS factory rifle.

Simple, reasonably accurate measurements setting up a SGS will get one closer than that...so 'adjusting' will only add another variable. More variables, more uncertainty, more potential for error.

Your favored JCN 'calibration' isn't a calibration. Neither is shooting factory ammo. It is at best a sanity check and I feel you are misleading people into doing unsafe things (inputting adjustments based on this method) with your recommendations.

Hot Core, you've had BS called on you how many times for this same nonesense... six?... seven??... eight times??? I've lost count.

I see you've resorted to your usual childish responses.

CDH understands calibration. NIST understands calibration. You do not. And you're not an EE, either.

Hey CDH, I've got a bit more time this morning, so let me ask you what "method" you would recommend for a person to use in order to "Calibrate" a HSGS?

I see you are rather adept at being (incorrectly) critical of the only real Methods of achieving Calibration. But, rather short on describing a Calibration Method. So, I'm ready for a few more good laughs.

quote:

Simple, reasonably accurate measurements setting up a SGS will get one closer than that...

No, this is simply the "Set-Up" and has nothing at all to do with Calibration. In the excellent 28kpsi example provided by Taliv, it is clear that the Method you and our resident lier adher to, leaves plenty of room for error being induced into the HSGS.

Come to think of it, I do believe that same "room for error" in taking the measurements has been pointed out previously in each of these HSGS threads that I've been in. At the time, you and our resident lier both said there was plenty of "Fudge Factor" built into the HSGS to compensate for any small measurement errors.

Of course, rational people understood that was full of beans. And they also realized if a Fudge Factor was "built in" then the "Claimed Accuracy" was also full of beans.

I'm hesitant to say you know as little about it as our resident lier who made The World's Most Ignorant Reloading Suggestion(sticking a sharp pointed object onto the anvil of a live primer and HAMMERING it out), but it appears you know nothing at all about Calibration.
-----

Suggestions like the one CDH made, and our resident lier, are the same kind of irrational trash that misleads people who just don't really understand how or why Calibration is necessary. They both lead people into "potentially" dangerous situations.

A HSGS (not Calibrated to a Known Standard) = Reloaders Pyrite (aka Fools Gold)

quote:

what "method" you would recommend for a person to use in order to "Calibrate" a HSGS?

In order to answer this question, to YOUR satisfaction, I need to understand what YOUR defination of calibration is. I am quite familiar with it...remember from our earlier conversations I am an EE for a engineering company specializing in industrial measurement...

What do you consider 'calibrated'?

Is your bathroom scale 'calibrated' to this standard? Do you trust the numbers it reads when you step on it? Are they good enough for the use you give it?

Is your speedometer 'calibrated' to this standard? Do you trust the numbers it gives you? Are they good enough for the use you give it?

The 'set up' as you call it, when done properly, will get you within a few %...and that is good enough for the vast majority of uses and well within the safety factors inherent in good reloading practices and good firearm maintenance.

I think explaining it to Hot Core again is an exercise in futility. I already posted the NIST procedure, and you already posted a practical example of calibrating PSI to within .02% using the procedure, without reference to a PSI artifact. He chooses to ingore all that, and more.

The simple answer to his question is: follow the NIST procedure.

The question Hot Core has to answer is: What reason is there that we should believe your silly notions of calibration, which firmly contradict NIST?

quote:

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

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:

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

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.

I have had a PT since they hit the market. Its a good tool. Works very well in standard chamberings where a factory round can be used for comparison. Works for Wildcats too but without the comparison To me this tool used in combination with a chronograph is invaluable in wildcat load testing.

I like it.

quote:

Originally posted by CDH:

quote:

what "method" you would recommend for a person to use in order to "Calibrate" a HSGS?

In order to answer this question, to YOUR satisfaction, I need to understand what YOUR defination of calibration is. ...

Hey CDH, I do recognize the old "Conference Room Two-Step" when I see it. Try to confuse the issue so the question never gets answered and the meeting attendees must be somewhere else.

But, fortunately for everyone on the Board who has the ability to "comprehend" Southern English, I've mentioned how and what Calibration is at least 3 and maybe more times within this thread.

However, to avoid another round of your dodging the issue, Calibration is done to a Known Standard.

Nothing tricky for you, simple Manufacturing Practices. Don't really concern yourself with how I think it should be done, cause that has been well covered above.

Just tell everyone how "you" think Calibration should be done.

Hot Core, you just refuse to see what is plainly in front of your face.

The burden is not on any of us to show why we follow the standard NIST procedure for such cases.

The burden is on you to show why your silly notions of calibration carry more weight than NIST's publications.

You have the links. Find something--anything--in the NIST handbook that supports your view. Or show us why your view is more correct than NIST's.

quote:

Hey CDH, I do recognize the old "Conference Room Two-Step

Call it what you like, I was merely trying to avoind another fuitile exercise in arguing semantics.

You seem to insist on a 'known standard' for proper calibration. The vast majority of the world is comfortable with using more indirect methods. It works, it is well proven, and it is well accepted. Your refusal to accept indirect calibration does not in any way change the fact that it works and works well.

To be 100% precise, calibration is anything the users can agree to as a satisfactory method. NIST has a set of rules that are quite good, and generally used in this country. In my business, I deal with a lot of international standards other that NIST. Have you ever heard of GOST (short for an otherwise unspellable, unpronouncable Russian word), SAMMI, CIP, etc? All they are are organizations that control a set of rules, and it is up to the rest of us to decide who to follow.

My assertation is thus: What you call 'set up' is quite sufficient for 'calibration' of the system to an accuracy and precision sufficient for the systems intended use. The rest is just arguing over semantics. The HSGS is sufficiently accurate (and SAFE) out of the box for its intended usage when properly set up, and proper setup is no harder than the process of reloading itself.

Just one more comment, then I'm done with this nonesense...

The mass of an electron is known. In fact, one of my physics professors was the grad student who did the lab work, and wrote the report that won Milliken the Nobel prize for measuring it.

How do you suppose they calibrated the scale? Did they bring in a standard mass from NIST (NBS in those days)and compare it? No. They did not. They charged small droplets of oil, and timed how they responded in air. The equipment for measuring the mass of an electron was calibrated indirectly by knowing the viscosity of air, and the force exerted by an electric field. Nobody used a standard mass to calibrate the equipment. I have personally repeated this experiment, and got a pretty decent number.

If that wasn't calibration, then perhaps you should try to persuade the prize committee to take back their award.

If it's within 10% and repeats, then it's of NO consequence.

I spent 189 bucks for a unit.. i can NOT reasonably expect the readings and resolution of a 50,000$ piece of lab equipemnt.

Much like a chronograpgh (do you "calibrate" it every time) that you pay 50 to 200 bucks for... and if it's within 1% (listed at 1/10 of 1%)... you are good!!!


jeffe

quote:

If it's within 10% and repeats, then it's of NO consequence.

I'll second that...as I stated in a previous discussion of this...the 2 most important factors in measurement are REPEATABILITY and SENSITIVITY. As long as it registers sufficiently small changes in input, and gives the same output each time with the same input, it is good.

Yup. Those are the two errors you can't compensate for elsewhere in the system. If you have those two, all other problems are solvable.

Hey CDH, I must hand it to you, that was the most worthless explaination I've seen concerning "Calibration" since I used to read the resident lier's old posts.

If that is what Manufacturing is doing in the USA today, it is no wonder every company is moving their products off-shore. It is even worse than I suspected.

So, best of luck to you.
---

For the rest of you considering buying a HSGS, let me recommend you glance back through the posts. Notice the problem that Taliv had and then reread CDH's recommendations. Basically CDH tells you to do nothing.

Then go look at what Sean did to insure his HSGS was actually Calibrated to a Known Standard.

Now sit back and decide for yourself which is the best Calibration Method.

Or, better yet, read the NIST handbook on calibration, and have a good laugh at Hot Core's silly and naive notions about calibration.

Well HC, excuse me for trying to inject some plain old common sense and simple logic into the discussion. Numerous people (not just Denton and myself) have tried the technical approach...and it obviously didn't work. I saw absolutely no point in rehashing old info, and you obvoiusly aren't into the technical stuff...sorta makes me think, "why am I wasting my time?" I doubt anyone reading this will have not made up their mind by now either...the simple truth is (NEWS FLASH) that things don't have to be calibrated to a known standard to be useful and meaningful! Get over it!

Oh, I'll hand it back to you...the crack about the state of manufacturing...very much an ASS_CLOWNish remark. Strikingly so...hmmmmmm

'nuff fun for one day.