This is my last post on this thread. Had to come back and agree with this portion of Brent's post concerning used rifles:

quote:

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Originally posted by Brent Moffitt:
...(metal)fatigue ...

This is the main problem with buying used rifles of unknown origan. If they have been subjected to repeated overloads, you could be the UNLUCKY winner, and with a normal load at that!!

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Absolutely 100% correct.

HotCore,

Sorry I was so pissy over this. I don't blame you for smackin me back.
I hope not to repeat much over again, I know you've posted alot on this already. I'm glad you sensed my frustration, but that's all it was. It is only that if you seen these in action you would hold a completely different view. You likewise obviously feel the same about me having not tried your method yet. I will, and will tell you what I find also. I hope to find something usefull to you and not to invalidate it or anything. I do agree you are probably always safe using your method if done with the meticulous methods you use. The exact interpretation of your data and repeatability is all that is in question "for me". In this respect you are just as right as I am to critisize me for my lack of trying you method to determine a max psi load limit. All my critisizm is simply based on the PRE of brass is potentially changed by many variables, of which I already mentioned. This "theory" is, I believe just more plausable than yours reguarding the strain devices ability to repeat.

I will let everything else go and not rehash it, unless you request I respond to something specific you had disagreed with.

You did however misunderstand a few things no fault of your own, but rather my lacking understanding of the english language. I am by far from the best speller as you have well seen, BTW you probably missed at least another twenty words I misspelled as well.

The label on the gage container says, "Precision Strain Gage" and Oehler also points out the the spelling referes to strain gage is different as well. Not trying to take a jab at anyones spelling ever, just thought to tell you about it. I really could care less how anyone spells on the boards, so long as I can understand what they mean. Most people, probably including you could care less either. In my case, it is truely indicative of my ability to spell. Many, I think, just rush through and type fast and get the point accross with not a whole lot of thought about it and are probably quite good spellers, I used to be but not any more. I just don't wright enough any more probably.

What I think you misunderstood was;

I said I measured 73k psi... That was on loads I worked up over max. No psi signs were observed until that point and some never were at all. More people work up loads this way and often exceed max recommended loads doing so, mainly because velocity is much lower as well. I only wish to let peopl know that in all my tests you are likely not getting those indicators until psi is probably higher than most think. Backing down 50-75fps will usually bring it into the "indicated" 60-65k psi range. I'm not just pulling this out of the air either. Basis; Factory ammo has always produced average psi within at least 5k psi of of SAAMI specs, period. If it didn't I would seriously have doubts about the systems abilities or the strain gages potential mounting problems pointed out. To even further substantiate the factory loads, book max loads are so close to max average SAAMI limits I just can't find any reason to think my gage is mounted wrong or it is giving consistant low or high data. However these things work out the psi and give us the numbers is beyond me, but I do KNOW factory and book loads are truely representative of what SAAMI has set as a limit for the given cartridge in question. All my testing has proven it to me that my gages are working perfectly to this end. If they were not I would get consistantly low or even high readings when establishing a baseline. I have found it to be on the money (within 5k psi) in all cases.

The point about wheather it averages 40k or a high 70k psi makes no difference;

If a baseline with factory and book ammo consistantly proved to average 70k psi on a "certain" gun it is far more likely that barrel measurements (thickness), gage bonding, or the gage itself would be suspect and causing the average psi to be moved up or even down (40k as mentioned before). If this proved to be a common problem, thank God it hasn't happened at all yet, I would have to resolve it. I only point this out because it still establishes a base line, even though the numbers are skewed. I have found everything corralates nicely with known data and factory psi's produced. If the chamber is stretched a certain amount by the factory loads fired and recorded as 62k psi, which steel happens to retain it's constant shape and elasticity unlike cases, it will take the same exact psi on the chamber to reproduce this psi number from the program. Stretch of the gage is the ONLY variable in the equasion here. The chamber is a constant thickness and has constant properties, the gage factor is constant and is calibrated which gives resistance readings to +-.3%. The gage is never stretched beyond it's elastic limits, unlike a case, so it gives repeatable resistance values over and over again. Nothing else ever changes in the equasion. If the gage is stretched less and gives a lower resistance it is a DIRECT result of LESS chamber pressure and is MEASURABLE as well.

If I established my base line at 55k psi and the factory and book loads were TRUELY producing 62k psi I would be in the same boat as the PRE method. Velocity with barrel length in mind should give you a BIG clue! I would have found this by now if it were in fact true and would not be debating the accuracy of it if I had. I am an advocate of what works, not what I "want" to work.

HC, are you not using factory ammo as a benchmark too, using PRE, you stated is is reliable on the first firing did you not? I don't assume it is all at a specific pressure, it just happens to always be in a specific range just below SAAMI ave. is all. That much I have gathered. The amount they vary is obviously not as much as you might think, it's not even worth mentioning.

Brent: �We are measuring a CONSTANT, not a VARIABLE as you are in PRE. The accuracy of my Oehler is consistant with everything I've tested and corralates to book loads, factory ammo, you name it.�

HC: Brent, I totally disagree that you are measuring a constant. Strain Gauges (that in fact are accurate) would indicate not only variations between Lots of ammo, but variation from shot to shot. Apparently the M43 is even LESS ACCURATE than I originally thought.

Again, you just misunderstood... I was refering to the barrel thickness and elasticity etc being constant in contrast to the case itself which is what you measure the stretch of. The case will get harder on each firing, it will not squeeze back to it's identical size each and every time, different lots will give different thickness and hardness and therefore expantion ratios. With the same gun and different brass you could have the same psi and different expansion, not the case with the same barrel and same gage using the strain setup. The PRE method is likened to an uncalibrated copper slug used in a copper crusher test, and then using the same one over and over to top it off. It is no wonder people used what they could draw some sort of parelell to help guide handloaders which had NOTHING close to the copper crusher method to use. Piezo is a step above this and offers the information to calibrate and design strain gages and programs taking the properties of barrel steel and thickness (which are constant) into account. A specific measured psi only causes a specific measured resistance in the gage and therefore the psi at that level has to be present to tell the program use this value. PSI reading are not the same, and differ from shot to shot, lot to lot, just as you'd expect they would. I have gotten shots that were exactly the same before but just here and there. As you indicate, there would be something wrong if it just read the same because there are too much variance in bass, powder, ignition etc to believe it if it did. I wish you could go to the range with me to test several guns with all kinds of ammo. THEN you'd see what I can't put in words, or don't know how to.

And HC, the unit is also under $1000.00 as many have already mentioned. If you want target sensors, amp and wire, later it can get up to around 2000.

Your experience with strain gauges, I'm sorry, I assumed you didn't know anything about them and that was just based on something you said reguarding the Oehler. I stand corrected. Was this first hand experience, what did you test with them, why were you testing and what was the results? I have not heard about them being used on anything else before. Obviously they do, but what?

Anyway, I will get a thin blade mic and try your PRE method along side the M43. Hope I can find a blade mic, not too common at the pawn shops around here. Anvil mics can be very cheap there though.


Take care,

HotCore,
I realize that you're done with this thread, so I'll say my peace and duck before someone starts criticizing my spelling skills, or my inability to use precision measuring tools.

There are apparent conflicts in what you say that I can't reconcile (or I'm going to have my reading comprehension criticized shortly as well).

Your major point of criticism (that you graciously corrected yourself on) was the perceived lack of calibration. That led me to believe you put value in calibration. But...

quote:

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Hey Chris, This will probably sound a bit off-the wall since you prefer to use numbers that you can relate back to psi, but yes and yes. It a person gains familiarity with CHE/PRE(and ALL the Pressure Indicators considered) you can eventually get skilled enough to be able to develop Loads using new, un-fired cases, without having ever fired a Factory round...

I've had a lot of 308Win rifles over the years and do not need factory ammo to develop Loads for a new one.

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Those statements off a more recent post leads me to believe that you don't feel you need calibration using factory ammo (the method you earlier said validated your PRE results). How do you reconcile different expansion behaviors of different makes of brass? From the following quote, you are obviously seeing this variation?

quote:

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ChrisF: "Using your 308 Win example, I wonder how well mushy Federal brass PRE correlates to Harder, thicker LC brass?"

HC: I don't remember well enough to quote from the top of my head. I have used some of the LC and I do remember the PRE varied much more than the Fed, Win and Rem cases.

But, the LC cases I had were from mixed Lots, so any inference that they were "bad" from my data would be misleading.

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Why is calibration not necessary in the face of such variation in brass behavior? While my plate is overflowing and it may take a while to actually do...I think I'll try to implement your PRE method with different brands of brass to see how it correlates with Strain Readings.

On the subject of sensitivity again...if you were to plot out your expansion over charge delta, you'd have 7 (or MAYBE 14) data points. My strain set-up could provide potentially 400! That is a huge difference in sensitivity.

Jon A, I did suspect a greater AUC, but am still stuck on the differing appearance of the brass from other powders of equal peak pressures (the RE15 and Varget brass was worse off). I'll be hooking up an O-scope shortly to replicate the Oehler's curve plotting and hope that illustrates something.

[ 02-09-2003, 13:32: Message edited by: Chris F ]

Just for the record, I've been 'lurking' on this thread which interests me greatly. I'm sure there are others also lurking and not posting.

I've 'known' HotCore for about 4 years here and other boards and if he says he's through, he's through.

In spite of the lack of an adversary for the debate, please continue.