I see Ken Oehler, the chronograph/ballistics lab genius, has joined the staff at SHOOTING TIMES. All y'all might enjoy reading his commentary on PSI to C.U.P. conversion in the current issue of said publication......

Hey El Deguello, I don't get the ST magazine. How about a synopsis for those of us that don't?
---

I'll stick by my regular position that there is no 100% accurate conversion between PSI and CUP.

quote:

Originally posted by Hot Core:
Hey El Deguello, I don't get the ST magazine. How about a synopsis for those of us that don't?
---

I'll stick by my regular position that there is no 100% accurate conversion between PSI and CUP.

OK, it's pretty simple - what he said essentially was that, after much labor, they were able to develop a computer model for converting C.U.P. to PSI & vice-versa, but a given model only worked accurately for ONE SPECIFIC CARTRIDGE -not more than one. So the whole idea was eventually ash-canned!

quote:

Originally posted by El Deguello:
...OK, it's pretty simple - what he said essentially was that, after much labor, they were able to develop a computer model for converting C.U.P. to PSI & vice-versa, but a given model only worked accurately for ONE SPECIFIC CARTRIDGE -not more than one. So the whole idea was eventually ash-canned!

Thank you for the info.

I seem to remember our old buddy denton tried his best to convince EVERYONE who would listen that "he" had developed a conversion for it when no one else in the world could.

Just another "denton doozie" - as usual.

Wouldn't surprise me at all to hear denton would disagree with Dr. Oehler though. Being TOTALLY WRONG has never deterred denton from telling everyone how he is the only person who has Ballistics completely figured out.
---

If any of you folks ever happen to see denton post, be sure to let him know Dr. Oehler says there is no PSI-to-CUP conversion. Then toss in Hot Core told you too - numerous times!!!

quote:

Originally posted by El Deguello:

quote:

Originally posted by Hot Core:
Hey El Deguello, I don't get the ST magazine. How about a synopsis for those of us that don't?
---

I'll stick by my regular position that there is no 100% accurate conversion between PSI and CUP.

OK, it's pretty simple - what he said essentially was that, after much labor, they were able to develop a computer model for converting C.U.P. to PSI & vice-versa, but a given model only worked accurately for ONE SPECIFIC CARTRIDGE -not more than one. So the whole idea was eventually ash-canned!

I have written a program for comparing running over something with a car to hitting it with a hammer, but it only works for Aluminum beer cans.
If Denton were here, he could put a strain gauge on the side of the hammer head, and measure the tire pressure, but would not look at the cans.
I Oehler were here, he would sell hammer strain gauges and tire pressure gauges.
If Hot Core were here, he would measure how flat the cans are with a micrometer.
If El Deguello were here, he would count how many times he can run over the can before it is flat.
If Saeed were here, he would admonish me for focusing to the honored Oehler's incentive.

"How to write a mediocre load book" second revision

Here's an interesting link...

http://kwk.us/pressures.html

quote:

Originally posted by Hot Core:
I seem to remember our old buddy denton tried his best to convince EVERYONE who would listen that "he" had developed a conversion for it when no one else in the world could. :rotflmo


If any of you folks ever happen to see denton post, be sure to let him know Dr. Oehler says there is no PSI-to-CUP conversion. Then toss in Hot Core told you too - numerous times!!!

It's long been known that no real conversion can be had for CUP to PSI.......as there's no conversion of apples to watermelons!

However.....I did record the formula Denton published here as I have use for "approximate" data.....not equal but approximate and the use of such data sets the demand for its accuracy...

here it is......but remember.....it's use is to be tempered with a sprinkle (or more) of salt!

PSI = -17,902 + 1.516 CUP

quote:

Originally posted by vapodog:

It's long been known that no real conversion can be had for CUP to PSI.......as there's no conversion of apples to watermelons!

However.....I did record the formula Denton published here as I have use for "approximate" data.....not equal but approximate and the use of such data sets the demand for its accuracy...

here it is......but remember.....it's use is to be tempered with a sprinkle (or more) of salt!

PSI = 17,902 + 1.516 CUP

I've compared Denton's formula with several measured pressures of numerous cartridges. The problem with his formula is the constant. The constant makes the formula "work" for all cartridges and all ranges of conversion. However, as Dr Oehler found it only really works for one cartridge with one specific constant. Denton's conversion works fairly well in the middle 1/3 of pressure rsnges. There are some discrpensies with the upper 1/3 and the higher higher the pressure the greater the discrepency. The lower 1/3 of the pressure range conversion with that constant is way out of wack.

In developing his formula Denton used published MAPs of SAAMI and CIP. The problem is he failed to understand the differences in the way the pressures were measured between the two sets of figures.

As noted; take any conversion between CUP and PSI with a grain of salt.

Larry Gibson

quote:

PSI = 17,902 + 1.516 CUP

That is way off for 45acp.

Matching an off set line to a curve can fit, in places.

But this is more than two variables.
It is not just psi and cup.
There are the cartridges that vary in size and shape.

Who would promote such an over simplification?
The same sort of person who would promote the application of strain gauges rather than looking at the brass for handloaders.
It takes someone smart enough to learn processes, but dumb enough to loose track of objective, and loose track of out of control variables.
That sort of mentally challenged person could personally insult Hot Core and leave AR in defeat, without ever really facing why he was wrong.

When I challenged Denton Bramwell on this forum to show the traceability to the NIST with the tolerances for a handloader with a strain gauge, and show the tolerance stack up, he could not or would not do it. From doing it myself, I knew the shape of the barrel and installation of the gauge have many variables that introduce errors that are a nightmare to quantify.

Denton, Hot Core, Oehler, and I are all Electrical Engineers.

We know that if an electrical measurement is not traceable with tolerance, it has no absolute measurement value. It only has meaning for relative measurements.

So then he is down to using reference ammo for partial calibration.
I asked for the accuracy tolerance build up on the NIST trace on the reference ammo.
He can't do that.
He can measure psi, he just doesn't know with how much accuracy, so the measurement has no meaning.

Still there are handloaders on the internet that respect Denton and there are voters that think Obama can fix too much borrowing and spending with more borrowing and spending.

So who am I speaking to?
I just hope there are a FEW smart people out there.

quote:

quote:
PSI = 17,902 + 1.516 CUP



That is way off for 45acp.

Yes....I believe it.....and as I recall it was stated to be relevant to center fire rifle rounds of medium capacity only.....such as .243 to .30-06. It was not intended to cover handgun and other smaller rounds or even larger rounds like the .460 weatherby.....I should have stated this with the original post of the formula......in all fairness to Denton.

quote:

PSI = 17,902 + 1.516 CUP

I show the equation as = -17,902+1.516CUP.

I never took the equation to be exact. It was simply an equation for a line that roughly fit the data. I use it enough to say a catridge is around 53,000 not 60-65,000. I sure don't try to say the number is 52,321.

quote:

I show the equation as = -17,902+1.516CUP.

yes....my error....I omitted the minus sign.....
and I changed my original post to reflect the correct post by Denton.

quote:

Originally posted by vapodog:

quote:

I show the equation as = -17,902+1.516CUP.

yes....my error....I omitted the minus sign.....
and I changed my original post to reflect the correct post by Denton.

It doesn't matter if you stick in a Division sign, write it backwards, or upside down - it still does not work. The derived data is just as valuable as that from an HSGS - totally worthless.
-----

Hey tnekkcc, Just noticed the age of the original post. Nothing like an old bunch of Buffalo Chips to get things fired up.

Playing with this thing using a diagnostic program could be interesting. I see this as PSI is PIS, but CUP varies with bore diameter (D). So if we take the constant, 17,902 that varies with bore diameter, we can add another independent variable. What we don't know is what multiplier (y) to apply to D, and what the new constant (k) will be.

First we re-write the original equation, PSI = -17,902 + 1.516CUP, in terms of CUP:

CUP = (PSI + 17,902)/1.516

Then we re-write the constant, 17,902, in terms of the variable D and its multiplier y, and a new constant, k:

17,902 = k + yD

Re-writing this expression in terms of y:

y = (17,902 - k)/D

This (17,902 - k) is simply another constant, K, and the 17,902 is just an artifact from Denton's original equation.

With data and a regression analysis module in a program like SPSS, we can solve for y and K in the data for each bore diameter and see if commonality of y and k among diameters is achieved. Our new equation is:

CUP = {(K/D) + PSI}/1.516

Of course, Denton's constant of 1.516 may not hold water, but we can solve for a third constant, M, in a new equation:

CUP = {(K/D) + PSI}/M

or

PSI = M*CUP - K/D

I would inquire about the availability of data, but my SPSS program is for Windows, and I've converted to Apple. But anyone else is free to experiment.

quote:

Originally posted by Winchester 69:
CUP = (PSI + 17,902)/1.516

Then we re-write the constant, 17,902, in terms of the variable D and its multiplier y, and a new constant, k:

17,902 = k + yD

Re-writing this expression in terms of y:

y = (17,902 - k)/D

With data and a regression analysis module in a program like SPSS, we can solve for y and k in the data for each bore diameter and see if commonality of y and k among diameters is achieved.

.

I for one am impressed with your approach. It only took 2 1/2 years for this thread to get something that looks good. Not sure I'll ever use it but this academic presentation is sure a breath of fresh air. roger

quote:

Originally posted by bartsche:
...this academic presentation is sure a breath of fresh air. roger

DAMN!!

thanks

.

Nope. You can manipulate it all you want and it still won't work - in a simple equation.

The only way to make it work properly is to develop a Variable Fudge Factor for each and every Cartridge.

And even then it would need a Range Factor built in as well.

The reason why it's so hard to convert CUP to PSI is actually very simple.
When using Copper units you need to thinks of it as the total over all measurement. PSI is a single moment in time.
Strain gauges to measure pressure are nearly useless. As you have zero knowledge of the properties of the barrel to the degree that is required to accurately measure with a strain gauge. It's supposed to be a simple setup but it's not you need to know the exact composition of the barrel steel and the exact heat treat performed. And I mean exact. the is just to many variables to ignore and you will accumulate error.
You need to think of CUP as and average and PSI as a peek. Once I understood how the two systems measured pressure I understood that any conversion between the two was nothing more then a guess.
I was all ready to go on the strain gauge thing Had my oscilloscope was looking at which strain gauges to get. Then I found the whole system is temperature sensitive as all get out. and requires calibration after any temp change. Resistance of the wires needs to be perfect because you are measuring a change as small as a thousandth of an Ohm. This can be effected simply by how you solder the wire to the gauge. Yes there are compensation circuits that can accomplish this but I'm not into that much damn work. to get a reading that is nothing more then a guess.
It's just to sensitive to be accurate at the range. Maybe in a lab but not at a range.
Unless you drill a hole into the barrel of your gun and install an electronic sensor you will have now way of knowing with any degree of certainty the pressure in you gun.

quote:

Originally posted by Hot Core:


The only way to make it work properly is to develop a Variable Fudge Factor for each and every Cartridge.

And even then it would need a Range Factor built in as well.

Just shows to go ya.When two guys like you and Winchester 69 put your heads together good things happen. 69?? roger

quote:

Originally posted by Hot Core:
Nope. You can manipulate it all you want and it still won't work - in a simple equation.

The only way to make it work properly is to develop a Variable Fudge Factor for each and every Cartridge.

And even then it would need a Range Factor built in as well.

Hot Core is correct. There is a "Variable Fudge Factor [b]for each and every Cartridge". That is why all posted pressures are MAPs. Those are "average" pressures which means they all have a +/- "fudge factor" to them.. Even with the SAAMI, CIP and military MPLM (Maximum Probable Lot Mean) there is a fudge factor.

Also, to say the psi is 51,456 or that CUP is 45,321 is not being realistic. The variables (even with Hot Core's vaunted PRE/CHE) are just to many from shot to shot to attempt such precision. Rounding off to 100s is even a stretch. If the + or - of a load is the industry standard of "2 standard errors" then even rounding off to the nearest 500 can be a stretch. This is why we most often see SAAMI, CIP and military MAPS rounded off to the 1,000s. When I post psi(M43)s I round off in 1,000s also.

Note; It is "reference ammuntion", not "calibration" ammunition.

Larry Gibson

quote:

Originally posted by kcstott:
Strain gauges to measure pressure are nearly useless.

Actually, a "Calibrated" Lab System, using Calibration Ammo to determine the Correction Factor(or Offset) is quite useful. The real problem is attaining the SAAMI Calibration Ammo, or Reference Ammo as some describe it. And having an environmentally controlled Lab to use it in.

quote:

As you have zero knowledge of the properties of the barrel to the degree that is required to accurately measure with a strain gauge. It's supposed to be a simple setup but it's not you need to know the exact composition of the barrel steel and the exact heat treat performed. And I mean exact. the is just to many variables to ignore and you will accumulate error.

Normally I'd agree, but once the Calibration Ammo is available, the Correction Factor accounts for that.

quote:

I was all ready to go on the strain gauge thing Had my oscilloscope was looking at which strain gauges to get. Then I found the whole system is temperature sensitive as all get out. and requires calibration after any temp change. Resistance of the wires needs to be perfect because you are measuring a change as small as a thousandth of an Ohm. This can be effected simply by how you solder the wire to the gauge. Yes there are compensation circuits that can accomplish this but I'm not into that much damn work. to get a reading that is nothing more then a guess.
It's just to sensitive to be accurate at the range. Maybe in a lab but not at a range.
...

Welllllll...., it is about time kcstott got a post correct.

I don't have a strain gauge. All I got is an SPSS program I can't use and no data.

Are the published PSI figures spurious? Actually, I wonder about the repeatability of CUP figures, considering that it is a purely physical system.

Yes. And CUP varies depending on where you look too.

I am not an electrical engineer, nor a chemical engineer (not involved in creating powders in any way), so I really have to ask this here:

"Exactly WHY is it again we are supposed to give a damn what the pressures are? Can't we just observe our cartridges in action, and the life of their cases? Then I've always decided for myself which loads I wanted to use, or not use, and never much cared what the pressures are in copper, wood, or bull pounds." In 60-odd years of shooting, that approach has never seemed to hurt me or the performance of my guns.

Best wishes, y'all.

B TW, this is the first time I've ever seen a really intelligent approach to this CUP/PSI equivalence question. If nothing else, it has absolutely convinced me to continue what I've been doing.

quote:

Originally posted by Winchester 69:
Are the published PSI figures spurious? Actually, I wonder about the repeatability of CUP figures, considering that it is a purely physical system.

This much I can say.....the confidence I have in the published PSI data on Hodgdon's website is far greater than any confidence I've ever had in any CUP figures from anyone.....maybe this will change but for now.....PSI is the best measure I've seen ever!

quote:

Originally posted by Alberta Canuck:
I ..have to ask this here:

"Exactly WHY is it again we are supposed to give a damn what the pressures are? Can't we just observe our cartridges in action, and the life of their cases? Then I've always decided for myself which loads I wanted to use, or not use, and never much cared what the pressures are in copper, wood, or bull pounds." In 60-odd years of shooting, that approach has never seemed to hurt me or the performance of my guns.

+1

A guy could get banned on lots of handloading forums for posting that.
This AR forum is different.
We get banned for being conservative politically, and no grief for spewing raw data from handloading overloads.

quote:

Originally posted by Alberta Canuck:
"Exactly WHY is it again we are supposed to give a damn what the pressures are? Can't we just observe our cartridges in action, and the life of their cases?

Given a nice, strong action you are absolutely right.
It's shooting some of those weak, antique-ee type firearms where it becomes a legitimate concern.

quote:

Originally posted by Alberta Canuck:
BTW, this is the first time I've ever seen a really intelligent approach to this CUP/PSI equivalence question. If nothing else, it has absolutely convinced me to continue what I've been doing.

What else is there to be said?

quote:

Originally posted by Alberta Canuck:
"Exactly WHY is it again we are supposed to give a damn what the pressures are?

If one wishes to get the maximum benefit from such cartridges as the 7 X 57, .257 Roberts, 8 X 57, 6.5 X 55, and even to a lesser degree the ld .30-06 and .280 Remington, then understanding the pressures most certainly help.....

For cartridges developed on the .308 case and most of the cases on the .30-06 family, the magnums, and the .222 family where the factory loadings are "up to par" with the brass abilities then factory loads and book listings will suit one just fine.

If I was reloading for such arms as the 1898 springfield, the .303 British SMLE, or many of the French, Russian, or Italian Milsurps as well as a very few Mausers and domestic bolt rifles (Savage 340) I'd want to have an understanding of pressures as well.

Same for Mi Garands, and a bunch of other arms that might be pressure sensitive and less strong than the brass case.....

Hey....it's up to you!

Does anyone on this forum have the knowledge and ability to come up with a series of graphs, PSI vs CUP, for every modern cartridge in their useable pressure ranges?

Now instead of individual cartridges come up with the same type graphs for small ranges of case capacities and calibers and still come up with good ball park figures? Examples

30 cal. , 2.45cc to 3.19cc.

Another:Perhaps 30 cal., 3.43cc to4.38cc.,

Another: 30 cal. 4.73cc to 5.62cc.***ect

for all calibers.

I don't know how usefull this would be to the average reloader , but how difficult would it be to do? The reason I ask is , I can think and envision in PSIG but I don't have a warm feeling or clue what CUP really represents as valued information. If this is true for me than I figure there are some one or two of us in the same boat. roger

Old age is a high price to pay for maturity!!! Some never pay and some pay and never reap the reward. Wisdom comes with age! Sometimes age comes alone..

Roger,
That's essentially how Denton came up with his "approximation" equation.....

Actually the equation isn't bad unless one actually reads the "equals" sign as an equality....and it cannot ever be as they are two different things.....and yes....I'm with you as it's a lot easier for me to relate to PSI than CUP.....so I use the "equation" for my own reference.....and nothing more.....one still must work up his loads!

I posted this a couple years ago and even that old slingshot shooter shooting moly-coated rocks agreed with it!

quote:

Originally posted by Hot Core:
[QUOTE]Originally posted by kcstott:
Strain gauges to measure pressure are nearly useless.

Actually, a "Calibrated" Lab System, using Calibration Ammo to determine the Correction Factor(or Offset) is quite useful. The real problem is attaining the SAAMI Calibration Ammo, or Reference Ammo as some describe it. And having an environmentally controlled Lab to use it in.

quote:

As you have zero knowledge of the properties of the barrel to the degree that is required to accurately measure with a strain gauge. It's supposed to be a simple setup but it's not you need to know the exact composition of the barrel steel and the exact heat treat performed. And I mean exact. the is just to many variables to ignore and you will accumulate error.

quote:

Normally I'd agree, but once the Calibration Ammo is available, the Correction Factor accounts for that.

I still say that measuring how much the steel moves has a tremendous amount of hysteresis involved and is not accurate unless you add in the fact of an exact barrel steel makeup (i.e. certified steel) an exact chamber dimension ( as close to the chamber size that was used for the calibration ammo) and as you said laboratory level controlled conditions. On top of the required calibration ammo. I just don't have much confidence in strain gauges after doing some research on how sensitive they truly are. I don't feel that one correction factor could be plugged into a formula to derive a correct reading. Multiple correction factors yes but a single one no.

As for the guy saying that observation of the case is all that is needed well not necessarily true. Yes a case bulge or primer flattening can be a sign of excessive pressure it does not say how much excessive pressure. Is it a little over pressure or a lot??? Is it soft brass?? an oversized chamber or an undersized case??
These are all things that must be known prior to saying the load is fine or over pressure etc. Condition of the case is only one piece of the puzzle.
Which is why most people and the market sticks with a chrono for measuring reloads. It's the least complicated way to get a number from your loads but it's still just a number and with out a calibration of some sort it is useless.
In reality if you truly wanted to see what your cartridge is doing you would need to build your pressure barrel and use a electronic sensor and a chrono in a temperature and humidity controlled room. Then get saami spec calibration ammo and calibrate the setup. Then shoot your loads through the system measuring pressure and speed along with the temp and humidity in the room and comparing it to the calibration data.
then and only then could you say with any reasonable amount of certainty that the load is safe or not.
Yeah I know My head hurts too.
This I why I just stick to the manual(s) and call it good for the most part.

quote:

Originally posted by vapodog:

quote:

Originally posted by Alberta Canuck:
"Exactly WHY is it again we are supposed to give a damn what the pressures are?

If one wishes to get the maximum benefit from such cartridges as the 7 X 57, .257 Roberts, 8 X 57, 6.5 X 55, and even to a lesser degree the ld .30-06 and .280 Remington, then understanding the pressures most certainly help.....

Hi Vapo- Am not trying to argue with you, but I don't need pressure figures of any sort to get the most out of any cartridge, SAAMI, foreign, old, new, or whatever.

That's why I work up specific loads for specific rifles, rather than use loads from a book.

I begin by taking a measurement of the volume of the case, select what my experience suggests will be an appropriate cannistered powder commensurate with the bullet, and start loading the cartridges low and shooting shooting them in the rifle for which they are intended. I may find I have made a mistake and began too high, but that usually shows itself immediately, and I drop down some more.

If everything looks okay with the starting load, I gradually increase the loads and shoot them, looking for negative indications in the brass or unexpected trends in the chronograph data. I keep doing that until I find a reason to stop.

At that point, I drop the load an amount based on the capacity of the case and, again, my experiences in the past. The I try using the load as a "probationary" regular load. If it continues to work well for me, I then put it on my "regular load" list for that specific rifle and cartridge.

No pressure numbers involved at any point. I began loading European cartridges I had never even heard of before that way back in the late 1940s and it worked fine. In the 1950s I became a bit of a Wildcat afficiando and used the same method there. Again, no problemo. In the 1960's it was on to really big bore British cartridges. No sweat. And so on ever since.

Of course, over time one gets a "feel" for loads, rifles, and components. And, if he wants a load which produces less than maximum output for a particular cartridge, he has very llittle development or "working-ip" to do.

Anyway, to me it really means squat whether a cartridge is generating 15,000 psi or 65,000 psi. What I care about is:

Is it safe in the chosen rifle?
Is brass life reasonable?
Is it accurate enough for the intended job?
Does it do its thing without harming my rifle with abnormal wear?
Have I got the load and process down to the simplest rigamarole that will accomplish what I want?
and a few other things.

For me a numerical indication of pressure never even enters the picture.

Others may enjoy thinking they have quantified everthing, but I prefer shooting to simulated pressure exercizes.

As you say, though, to each his own.

I wish you a Happy New Year and many more of them.

quote:

Originally posted by bartsche:
..ranges of case capacities and calibers and still come up with good ball park figures? ... but how difficult would it be to do? ...

Hey Roger, I have the Barnes #1 Manual and it has Cases Capacities of Water listed next to the Case schematic. Don't know if they still do it or not in their newer Manuals.

Also all the Internal Ballistic Software Programs have a Case Capacity Value. As you mention though, they are only approximations because not all brands of Cases for a specific Cartridge have the same internal dimensions.
-----

Hey Vapo, Can't remember if I mentioned(aka Oldtimers) that KY has "Banned" Sling Shots, on your person, during Squirrel Season.
-----

Hey AC, If that works for you, I'm all for it.

As for me, I'll stick with the time-proven, always-reliable, never-fail CHE & PRE Methods because they do the following:
1. They allow me to use the $$$Millions$$$ Factory Pressure Labs to set my Benchmark Standard.
2. PRE always works and CHE is an excellent backup.
3. The two Methods address all the concerns listed in kcstott's last post.
4. They provide First-Hand Pressure Indications when an HSGS can't.
5. And the Micrometer is 1% of the (totally wasted) HSGS cost.

Hot Core.
I don't know your experience with measuring tools and measuring tenths of thousandths of an inch. I personally have experience measuring to 50 millionths of an inch and know how hard it is to get a good reading at that level. It's a pain, It's time consuming, But it can be done with skill and practice.
Others reading your post should be advised that measuring to the forth decimal place takes some getting used to. I personally would recommend Getting a few gauge blocks and calibrate your fingers and the mic. There is a given amount of feel involved. I personally have never relied on the ratchet to get my reading But other tool makers I've worked with have and can get the same reading I get within 50 millionths of an inch. So to each their own I guess.
Now one other thing that needs to be advised Measure the part at the same temperature that you initially measured it at, as best you can control. Brass expands at .00001" per degree F of temp rise so 10 degrees of rise would give you an extra .0001" Just a be advised to others that may want to try this.

Hey Kerry, You are correct in your concerns. Fortunately it does not take a person long to be able to repeat a 0.0001" reading. Most folks can get the hang in about 20min or less. Just depends on the person.

If it is not clear in the Link, people should not expect to measure the CHE/PRE on a group of Cases and have every measurement the exact same. Same as they should not expect to fire a group of Cartridges over a Chronograph and get every reading the exact same - it is not going to happen.

They should be looking for a Trend as the Pressure Increases with their Loads and STOP when the specific points are reached as described in the Link.

If they follow those instructions, they can enjoy the same benefits as thousands of old-time reloaders have for many generations. Those benefits are being able to see the Pressure rise as the Load Increases and knowing when to Stop adding Powder.

Nothing tricky about CHE & PRE, they work and work well, just as they always have.

When I measure CHE I put a dot on the case with a black magic marker and then measure over that dot with the blade micrometer.

After firing the dot is still there and I can again measure over the very same place on the case diameter.....no rocket science required here!

In the '70s I was a tool and die maker and learned to use many kinds of micrometers surprisingly well.....some were better than others for sure but the best I ever used was a $12 0-1" Mitutyo that I actually could measure to .00005 and that was confirmed by a $1500 Pratt and Whitney super mic! It does require a bit of finess but .0001 readings can be done with a capable micrometer.

I can tell you how sharp a Siwash hook is! roger

quote:

They should be looking for a Trend as the Pressure Increases with their Loads and STOP when the specific points are reached as described in the Link.

Exactly.... The trend or pattern of events is what you're looking at not one dimension or one number.

quote:

Brass expands at .00001" per degree F of temp rise so 10 degrees of rise would give you an extra .0001"

If you stand there holding the mike a while it will change too.