I'm pretty sure this will open a few cans of worms, but it may be worth it. Forty-odd years ago, in one of his books an English firearms writer of considerable note mentioned that he had experimented with making a cheap but useful pressure indicating tool for use in his loading of shotgun shells. And, he said it worked pretty well for its purposes.

Basically, what he did was to "corrugate" some plastic material about the thickness of a playing card to make it a particular, greater, thickness.

Then he put a very thin and weak adhesive on one side. Next, he used a die to cut round "pasters" out of the material and to make a hole in the middle where the primer is in a shotgun shell.

Then he would carefully measure the thickness with a .0001"mic and record the reading. Last, he would stick a paster to the head of a shotgun shell, place it in a gun, and fire it.

At first he fired it with industry standard recognized common loads, for which the pressures had been published by the manufacturers. He then carefully removed the pasters from the shells and measured the thickness of the pasters. From the measurements he made up a table showing which thicknesses indicated which pressures.

Of course, the pressures weren't exact. But they did correlate well with the results from other cartridges and other guns....

That is, if one fired three different makes of shells that were rated by their manufactuers as having pressures in a particular range, they would show similar thicknesses after firing, even in three different guns.
By doing so with factory cartridges rated at different pressures, he found he could use the pasters to know which broad pressure group any particular shell would fall into ,in terms of useful data.

I.e., He could tell with his mic whether a shell was performing at less than 10,000 p.s.i., 10,000 to 15,000 p.s.i., 15,000 to 20,000 p.s.i., or some greater (and potentially dangerous) level. In more general terms, they would indicate very low pressure, low pressure, moderate pressure, and high pressure.

He then commonly used those pasters with good success in determining where his handloads were performing with other than published loads .

He also expressed suprise that no commercial firm had ever picked up on manufacturing such pressure "pasters", "washers", or whatever one might call them, together with a table for using them, for inexpensive sale to handloaders.

He opined it would be a lot better than just "by guess and by golly" for knowing when one was approaching a safe "maximum" day-to-day working load. If for instance, a particular paster was rated at indicating 53,000-to-59,000 p.s.i. when it measured a particular thickness after firing, loaders of modern high-intensity magnums might well find such a paster invaluable in developing their loads.

Of course there is considerable difference between the 12 gauge shotshells he was loading and high-intensity rifle loads. Such pasters would do nothing for telling a person exactly what pressures he was getting from his loads. But if they could be manufactured of a modern plastic or metal alloy which would accurately indicate broad ranges of say about 5,000 to 7,000 pounds, they could help an awfully lot with a large variety of handload evaluations.

Also, pressures at he bolt face really aren't anything like the pressures at other points because of brass adhesion during firing to the chamber walls. But, we don't have to call what they are showing "P.S.i." They could be called "bolt face units" or anything else which would identify them easily in discussion or record-keeping.

And with modern materials, I wonder if that just might be possible? What do you guys think?

Do you find such an idea feasible? Would you buy them if they were available?

BTW, a last interesting bit....he found them so dependable he said you really don't even need a mic to read the ones he made for shotshells. Their visual differences with loads of different levels were enough to tell which pressure range they were indicating.

I think the only thing you would be measuring via your method would be "bolt thrust".

quote:

BTW, a last interesting bit....he found them so dependable he said you really don't even need a mic to read the ones he made for shotshells. Their visual differences with loads of different levels were enough to tell which pressure range they were indicating.

I think anything that would visably show shotgun pressure differences would be worthless for rifle and pistol pressure reading. Shotguns work in the 10-12K max psi range, even cartridges like the 45acp operate at a higher pressure.

What I think is this is another thread for HC to hi jack for a lecture on CHE and PRE.

quote:

Originally posted by Rusty:
I think the only thing you would be measuring via your method would be "bolt thrust".

First of all, Rusty, it is NOT my method.

And as I said in the post, pressure against the face of the bolt might be what it was measuring. But so what? Is bolt thrust not related to the pressures the cartridge is developing?

I can see two major things the person I was referring to obviously was not intending to measure, which I know his tool could not report, no matter how generally....those would be the time under the pressure curve and the shape of the curve in realtionship to the maximum pressure it registered.

quote:

Originally posted by Ol` Joe:


I think anything that would visably show shotgun pressure differences would be worthless for rifle and pistol pressure reading. Shotguns work in the 10-12K max psi range, even cartridges like the 45acp operate at a higher pressure.

'Ol Joe- I agree that things which might work for indicating general levels of shotgun pressures very likely would not be useful for rifles.

But how about the same concept but with a different wafer material...maybe even several different wafer materials to indicate different pressure ranges?

You know, Tempilaq works similarly for temperature readings...the mix which will melt at one temperature is not the same mix that will melt at a higher or lower temperature.

So the questions remain...IF an inexpensive set of discs could be developed...one disc which would show whether a shot had a peak pressure in the 33,000 to 40,000 psi range, another which would show if the shot was in the 41,000 to 48,000 range, a third disk which would show if a shot was in the 49,000- 56,000 range, and a final one which would indicate a shot within the 57,000-64,000 psi range, would they be of any use in your opinion?

Would you have any interest in buying such a set if it sold for somewhere under $20, for instance?

There is such a tape available. "Tekscan".
I changes color with stress. I have used it
to see when the case sets back.
In a oiled chamber it comes back at once.
In a dry chamber (35 Rem) it stays forward
until about 40 kpsi then comes back.
This requires a chamber with a bit of headspace. You could move the shoulder back a bit. the read out is sort of crude probably
somthing like +/- 10%.
Good luck!

quote:

Originally posted by hawkins:
There is such a tape available. "Tekscan".
I changes color with stress. I have used it
to see when the case sets back.
In a oiled chamber it comes back at once.
In a dry chamber (35 Rem) it stays forward
until about 40 kpsi then comes back.
This requires a chamber with a bit of headspace. You could move the shoulder back a bit. the read out is sort of crude probably
somthing like +/- 10%.
Good luck!

That is interesting news. Do you have any idea how thick it is? Most guns have "some" little bit of headspace to spare over new cartridge cases, as SAAMI minimum chamber specs are larger than SAAMI maximum cartridge specs.

Of course the amount of "whap" against the bolt face is one of the primary things handloaders should be interested in. Most damage to rifle actions, for instance, starts to occur with locking lug recess set-back from repeated blows with loadings that are only marginally too high. If a person could detect loads in such too high pressure ranges by using the tape, it could be very handy. From a practical standpoint, it doesn't matter how much exactly "too high" pressures are. Any amount "too high" is too high for practical use.

Though of course no one wants to blow a barrel and/or receiver ring apart, that almost never happens in rifles except where there is an innate flaw or manufacturing-induced "shear line" in the steel already. For it to happen in an unflawed piece of barrel steel probably requires pressure well beyond the point where lug recess set-back would have already occured.

Back to the tape, does it have "degrees" of colour change so one can "guesstimate" different pressure ranges? Or does it just change once when a certain pressure is reached?

Do you know where it is currently available and the approximate cost per unit?

quote:

"Inexpensive" -- "pressure-reading tool"

Mutually exclusive terms.

quote:

Originally posted by Jim C. <><:

quote:

"Inexpensive" -- "pressure-reading tool"

Mutually exclusive terms.

Not necessarily. Since the tip was posted above about the tape, I have located the manufacturer of the tape mentioned. Their most common tape is used a lot like litmus paper....that is it changes colour intensity (shades of red) depending on the pressure sensed (applied).

I am now in discussion with them about a modified tape for the exclusive range of interest....that is, from 10,000 psi to 70,000 psi. (Their most commonly made tape right now shows pressures from 1,250 psi to 43,500 psi. That would be fine for pressures from perhaps .22 WRM through .30-40 Krag (in Krag rifles), but not for hotter rounds.)

Don't know how long before I will be able to report any more, but if and when, I will.

It may turn out we can't identify a supplier, but kissing the idea off without trying definitely won't locate one.

P.S.: It turns out that applied ready for use, the tape can be as little as .004" thick. Depending on the gun and cartridge case, that might work just fine with no modification to the case. In other situations, it might require a very slight bit of extra sizing.

P.P.S.: It also turns out the tape is commonly used already in structural load-bearing engineering, and race car engine & chassis construction, among many other uses.

You have to keep in mind what you are measuring. The total thrust would be the areas
of color change. In other words the localized
pressure depends on how the surfaces match.
I suppose you could say it's 25% red, 60% pink
etc. Once you have the force then you could do
a calculation of chamber pressure.
Note the pressure between the case head and
the breech is not the chamber pressure.
I want to repeat the statement about a dry case staying forward until 40 kpsi or so.
That is why a with headspace a low pressure load will have a projecting primer. When the case does come back it has the same force oiled or not. This was supported by the (crude) tests
I ran, and a finite element analysis by OK Shooter. A final observation. With an oiled case
the case comes back at low pressure and expands
forward. This avoids the stress ring where the neck stays forward and the case expands to the rear.
Good Luck!

I understand what is being measured, It might also be possible to apply tape to the side of a cartridge (part of one side), if the cartridge was sized a bit smaller than normal or otherwise impressed to create a space for the tape. In that instance, one would be able to do inexact measures of chamber pressure....and one could do the same with factory cartridges as a "control".

A series of six to 10 shots with a load should give a good average "guestimated" figure... certainly likely to be better than the "no figure" system most of us now load with. Again, the goal/purpose wouldn't be to know exactly what the pressure was...simply if it appeared to be within a "safe" range.

Interestingly enough, the English cartridge makers such as Kynoch used to load to "bolt thrust" pressure standards, using oiled cartridges, NOT to chamber pressure psi standards such as are used by American manufacturers. That's because they felt it was a more practical approach, considering what makes rifles fail, and how they fail. When all the cartridges measured are oiled, they DO come back with different forces, depending on the load.

Anyway, it will be interesting to see if a tape with the pressure span I am interested in is possibly available. If it is, I hope it will be inexpensive enough that a person can buy it cheaply enough to do a lot of experimenting at little cost.

Quien Sabe?

AC,
Sorry didn't mean to imply that the method was yours. Let me try to rephrase. . .

The method you discribe looks very much like the copper pellet crusher method used by the British on their Nitro cartridges. That method measured bolt thrust. There was an extensive thread on the forums a year or so ago concerning that method.

The pressure tape in existence would suite me just fine. The real question is, where can I get some? Chamber pressure itself is of no real concern - it's the effect of that pressure on the case itself and of course, the bolt face (locking lugs, actually).

As an anecdote - I know of at least one rifle that blew up on the factory test range (308 fired in a 270). The receiver ring split, letting the barrel fly down-range. The barrel was still serviceable! (I've no idea of the damage to the lugs or abutments).

The York-Cantrell system went the way of many good, early ideas. I'll have to see if I can dig up their owners manual and read up on it. I have one somewhere here in the house.

Don

It occured to me I could simply look it up on the net! Prescale™ Pressure Indicating Film - a Tekscan product.

Using the tape on the case body might not work as there are shear forces involved. Still worth a try!

I would suggest that the Tekscan product should be used with the same case to get relative indications since the case and bplt face are not flat surfaces. Perhaps a quality factory round followed by load development in the same case. And of course, a well lubed case.

Taking the principle back to the original suggestion, perhaps a 'development' case could be relieved at the head to accomodate a lead or soft copper 'washer' that makes up the relieved amount. The degree of expansion on the washer OD could be used to infer a relative thrust.

Ther is a stuff called 'Plasti-Guage' which is just a rounf plastic 'wire' which crushes to fill a clearance, the width of which indicates the clearance. (Not load measuring, I know but along the same lines).

By the way, I do see a small problem with this type of pressure inference and that is that 'plastic' material, including lead, flow under pressure and time so the indication would be influenced by mean pressure as well as peak pressure.

I am most intriged by hawkins findings with dry versus lubed cases. I have long held the view that this is what was happening.

What about making a softer metal 'adaptor' to seat a small rifle primer in a large primer pocket and measuring the 'adaptor pocket' expansion? Or machining out the pocket so as to use a LR primer?

303 Guy: The sequence is that the primer firing
pushes the case forward, and the primer comes back against the breech. With headspace a lower pressure load will allow the case to stay forward and the primer protrude. With higher pressures the forward portion of the case will stick and the case will stretch back. The primer
will have bulged a bit befor the case comes back
over it giving it a "rivet" look. With an oiled
case the case comes back then stretches forward avoiding the stress ring. Once the case comes back it has the same force against the breech oiled or not.
P.O.Ackley in his book told of firing a 30/30
Improved in a 94 Winchester with out a locking bolt. The breech stayed shut which he attributed to the straight improved case. Actually it was probably due to the low pressures.
Take care!

quote:

Originally posted by 303Guy:
The pressure tape in existence would suite me just fine. The real question is, where can I get some?

Hi again-

That product is actually made by Fuji Film according to their corporate site. I don't know how large a minimum order is required, but I would think the Fuji Film importer/distributor for NZ (likely in Aukland) could supply it if it was made worth their while to order some.

I can see where a "shear" force MIGHT be a problem when the tape is used on a factory round, as the factory case-length is sufficiently short to allow chambering in any commercial chamber of that nominal designation...and will result in some case lengthening on firing. Still with both the case and the outside surface of the tape oiled, it might be no problem at all when the tape is placed on the side of the case. It does not have to be either a long or wide patch of tape....just put in the same location on cartridges, the readings of which are to be compared.

As for handloads, because they can be fireformed to fit the chamber completely except for springback, and then oiled, I would expect even fewer shear problems.

What I find interesting, but not suprising, is the number of reasons folks seem to feel the idea should be shot down at launch rather than tested. Well, if I can find anything that reads in the range I would like to use, I will test it anyway. Hell, it is only time & money, and it just might be of some limited use.

Especially if any useful suggestions were considered. (That comment is definitely NOT aimed at you, .303Guy. I appreciate your always useful and helpful comments.)


As to the idea of using lead or other metal washers on the base of the case...that is what I was referring to when I first asked the question here. The original tests by the writer to whom I referred, used washers or discs the outside diameter of which were the same as the case rim, and which had a series of decreasingly smaller concentric circles cut into them, much like rifling is cut into a barrel. That left erect circular "lands" on the exposed surfaces of the washers. The pressure of firing tended to collapse the "lands", thus reducing the "thickness" of the washer. The reduction in thickness, compared to the reduction caused by factory loads on similar washers, provided him his comparison info.

It is, of course, true that the entire load over time (over the pressure curve duration) all acted to "do the dirty deed", but that is of no concern, as the same happens with bolt lugs and their recesses when firings occur with any rounds.

The reason the tape discussed here may not show anything but peak pressure is because once the peak is reached, pressure begins to fall, rather than increase (by definition). The process by which the tape works halts once that highest pressure is reached , so any further pressure application does nothing to the tape colour, regardless how long it is applied.

As to receiver rings splitting....yes that can and does occur SOMETIMES, but not from pressures any sane handloader would be likely to develop. Ackley, in his action blow-up tests showed just how difficult that was to do. Those tests are in one of his books, but whether Volume 1 or Volume 2, I can't recall off-hand.

Best wishes,

AC

quote:

P.O.Ackley in his book told of firing a 30/30
Improved in a 94 Winchester with out a locking bolt.

I read about Ackley's tests. He did not fire that rifle on his shoulder! (He was far too clever a man to do that ).

quote:

Once the case comes back it has the same force against the breech oiled or not.

I have a theory that the bolt face load could actually be greater with a dry case because the case 'binds' in the forward position until the pressure is high enough to cause it to 'let go' resulting in a suddenly applied load. However, your tests do not support that one.

quote:

The pressure of firing tended to collapse the "lands", thus reducing the "thickness" of the washer.

The broadening of the collapsed ridges could also be used to interpret the degree of flattening. Mmmm... I did read that part in your first post, AC, but forgot it! You're right in all respects about the pressure film. Someone must be using it over here. It has a wide range of applications, it seems.

You know, I recall seeing something on a case wall mounted copper crusher. An indent was made to accomodate the copper pellet.

I have tried making an indent on a point on the case wall then observing the degree of flattening out on firing. It seemed useful only at pressures below what the primer would indicate.

quote:

You know, I recall seeing something on a case wall mounted copper crusher. An indent was made to accomodate the copper pellet

I don`t know they are all this way but, the crusher method used in most labs (SAAMI/CIP) has a hole drilled in the chamber wall and the copper pellet held against the case wall by an anvil. At least this is the set-up I`ve seen pictured in readings on the subject although SAAMI offers that the hole is opitinal.

I believe this "option" may due to the use of strain gages as a alterative way of pressure measurment and the barrel set-up they illistrate is for both systems..Could be wrong though.
Here is a down load of SAAMI cartridges and their pressures, chamber and cartridge drawings and test methods. The crusher method is described and shown on pg 97. The piezo set-up is a few pages further down.
http://www.saami.org/Publications/206.pdf


Edited to add this link to a listing of SAAMI and CIP pressure ratings and an write up on the bottom of the page on how they test. Some may find it interesting. http://kwk.us/pressures.html

quote:

(Their most commonly made tape right now shows pressures from 1,250 psi to 43,500 psi. That would be fine for pressures from perhaps .22 WRM through .30-40 Krag (in Krag rifles), but not for hotter rounds.)

Fasnating idea.