The Accurate Reloading Forums THE ACCURATE RELOADING.COM FORUMS Guns, Politics, Gunsmithing & Reloading Reloading Re: pressure signsGo | New | Find | Notify | Tools | Reply | |
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Denton, Your character HAS rounded lately. By your little table do you mean?: "From published data, and from my own tests, I estimate the standard deviation of the random error (sigmaE) of the available pressure measurement systems to be CHE method: 7,500 PSI PRE method: 6,800 PSI copper crusher method: 1827 PSI published piezo PSI method: 1366 PSI PressureTrace strain gage: 667 PSI" I was thinking of a comparison that included not only the pressure measurement error, but the chosen maximum pressure limit error. Hot Core, I use extractor groove measurement when the real load limit is a chance the primer may fall out. The only reason I measure extractor grooves, is that it is the easiest way for me to measure, with dial calipers, how close I am to a primer falling out. Primers may hang like chads, but the relationship between extractor grooves and primer pockets is predictable. | ||
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Quote: Absolutely. I did finally remember the old Logic Problem last night. I'll start a thread on it. | |||
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Quote: Yes, exactly. These are the key numbers that describe the random error in each system. Random error is usually the nastiest source of measurement system error, and limits the overall usefulness of the system. The CUP and PSI estimates are derived from data published on p91 of the Lyman handbook. The others are from experiments that I performed, which anyone can replicate. PRE and CHE flunk the standard Interclass Correlation Coefficient test of repeatability by a continent and a half. Using the usual statistical rules, if two cases show exactly the same pressure ring growth, then the two pressures that generated the growth are within 27,200 PSI (4 x 6,800 PSI) of each other.... nowehere near a trustworthy level of repeatability. You can pull the error down with averaging, but the numbers required get out of hand before you get decent repeatability. Hot Core, how much peak pressure does your fravorite load generate? You claim to have a calibrated, exactly repeatable system. If so, you can easily give us the answer and the methodology. Ken Waters said he couldn't do that. Since you have now exceeded Ken's ability, we are eagerly awaiting your answer, and details of your method. Please answer quickly.... I don't think we can stand a long wait. Quote: Absolutely true, but irrelevant. The growth of the primer pocket is very highly correlated with groove growth. If you know how much your groove grew, you know how much your pocket grew. Therefore, what? | |||
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Travis, I am an Incredible Hulk fan. You know, "Now Hulk SMASH spider sense!"    "Spider sense" sounds scary to me, but if it works for you I am glad. ASS_CLOWN | |||
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On a similar note, Here is a report on case appearance vs pressures found by strain gage. Charlie Sisk has the thread going on 24 hr campfire today. There are no formulas or statistics given but I found it eye opening.............. http://www.24hourcampfire.com/ubbthreads/showflat.php?Cat=&Number=309519&page=0&view=collapsed&sb=5&o=14&fpart=1 | |||
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I'll jump right in where angels fear to tread... Beginners guide to pressure signs: Be aware that any individual primer brand may not look at all similar to another primer brand at the same pressure. Until you know what the specific brand of primers look like at " some pressure ", this is really misleading, and defining " some pressure " is at best, a guess. Start at the low end. Reload the case several times. If the primer pocket gets loose, and the primer falls into it when you reload it fewer than 3 ( three ) times you need to back off a little. This is considerably less scientific than measuring the case head, but tells you exactly the same thing ( when the case head expands the pocket will get loose ). Do not go over what the manual lists as "max" for your combination, until you are willing to accept the responsibilities for your actions, and your " spider sense " tells you it's OK... For most combinations the manuals err on the safe side, and the powder and bullet mfg. tech lines will be glad to assist you ( and they have real pressure tested data ! ) I will suggest you stick with " pressure tested " data until your " spider sense " is finely honed. And watch for loose primers, or other obvious defects. " spider sense " I am really surprised none of you other guys even mentioned that... Travis F. | |||
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Quote: Denton, E [total] = E [measurement] + E [pressure limit vs real limit] Here is the way to compare pressure error for advanced handloaders for their own guns that are substantially stronger than the brass: If the real limit is short brass life i.e. loose primers, then we must consider the error that is the difference between the assumed limit e.g. 65,000 psi and primer pocket growth e.g. 69,313 psi = 4,313 psi CHE method: 7,500 PSI + ? PRE method: 6,800 PSI + ? copper crusher method: 1827 PSI + 4,313 published piezo PSI method: 1366 PSI + 4,313 PressureTrace strain gage: 667 PSI + 4,313 extractor groove measurement: ? + ? primer pocket measurement with pin gages = "brass variation" + 0 Considering "brass variation" the sample size shot at the range is too small Finally .the scheme for load reduction [below the lowest charge that produced pocket growth] contains a long list of errors, like pressure is not proportional to powder, the powder charge accuracy assumes 2 cups of coffee that morning, etc. | |||
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Quote: Hey Clark, I disagree with you completely on the above. If that were true, then how is it he had ZERO concept concerning the fact that the Case is the "Weakest Link" in the firing sequence? I know I've mentioned it numerous times in the past when discussing CHE/PRE as the discussion headed toward getting "First Hand" information directly from the "Weakest Link" in the Firing Sequence - the Case. That was in comparison to "Second Hand" information coming from a HSGS Set-Up using "guesses" for barrel thickness and absolutely no ability to Calibrate the fiasco. So, no I really don't agree with you on that AT ALL! ... HSGS = Reloaders Pyrite!(aka Fool's Gold) | |||
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Quote: Hey Ol` Joe, Darn shame Mr. Sisk wasn't using CHE and PRE at the same time. He wouldn't have blown-up the barrel then, unless he just wanted to. Looks like he is going to have to toss that barrel. Of course, once a HSGS is hooked to a barrel, trashing it is the best thing to do anyhow. HSGS = Reloaders Pyrite(aka Fool's Gold) | |||
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Quote: Hey Travis, Your first part is an excellent method in the "High Pressure" cartridges found in modern Bolt Actions. Only problem is in some of the old "Low Pressure" cartridges, you really don't want to get to the "Loose Primer Pocket" Pressure level. I'm not up on this "spider sense". Could you expand on that a bit? Sure don't want to be caught not knowing about the latest and greatest. | |||
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Hey Hot Core, how many peak PSI does your favorite load produce? You claim to have a perfectly repeatable, reliable, calibrated system for measuring pressure. So you must have the answer. We're waiting. | |||
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Clark... Not sure I exactly understand your post. I think we are in agreement that sample size is the limiting factor for PRE and CHE. It's not that they can't be made to work. It's that the sample size is large to get a decent answer. So, if you're using PRE, and you are worried about going over SAAMI limit, you have to stay two standard deviations, 13,600 PSI, below your target, to be sure you don't go over, due to uncertainty in your system. SAAMI does something similar with their pressure measurements. The actual limits are higher than what we generally see published (though not by a whole lot). When they do their 10 shots, they take the SD of the sample, and back down 2 SDs from the real limit, to ensure that they aren't over. | |||
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I am saying the SAAMI limit contains an error that should be addded to the measurement error for a total error in evaluating a shot fired. The advantage for the individual loader is that he can null that SAAMI limit error if he can evaluate the shot fired relative to the real limit [the change of brass that could allow the primer fall out]. If the .223 real limit is 86,427 psi, and SAAMI is 55,000 psi, then the SAAMI limit error is 33,427 psi. From AC's post:  | |||
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If the tool you have is a hammer, then you'll try to make all problems into a nail. Unfortunately, it's true. I do stats so much that everything starts to look like a stats problem. If you look at the pressure that a given load will produce in a large variety of firearms, using different lots of powder, and different temperatures, you PROBABLY get a normal curve. You also have a bunch of different limits, such as the pressure needed to set back the lugs, the pressure needed to "stick" a case, the pressure needed to split a neck, etc. Each of these has their own distribution. The question then is, what is the max pressure you can run without the right side of the pressure distribution touching the left side of the first limit it comes to? If you use a high resolution measurement system, it's easier to see the limits. If you have a low resolution system, then you have to allow a couple of SD's of measurement system error as a buffer, and you can't get the distributions as close to each other. I expect that some kind of rigorous thought went into the SAAMI specs, but, as far as I know, they have never published their method. At the moment, I choose to simply take them as a "given", even though I can see some holes in what they have published. | |||
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