The Accurate Reloading Forums THE ACCURATE RELOADING.COM FORUMS Guns, Politics, Gunsmithing & Reloading Reloading Re: How do I figure out pressures?Go | New | Find | Notify | Tools | Reply | |
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Quote: NO, assuming the chamber and bore are of a like tolerance and finish. Quote: The pressure curve (pressure at any given point/time) will be the same until the bullet is clear of the barrel. Longer barrels yeild higher velocities because there is a longer time for the gas to accelerate the bullet (more "work under the curve") Quote: Yes. It builds to a peak as the powder is fully consumed, and than diminishes as the size of the cylinder increases (the bullet moving down the barrel). Quote: Within practical dimention limits, NO. If the barrel is extreamly thin walled (under recogmended minimum wall thickness) it might due to the barrel balloning or bursting. Quote: | |||
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Calibration: There are only seven fundamental, or "primary" physical quantities. Mass, electrical current, time, distance, luminous intensity, etc. Only one of these, mass, is presently defined by NIST in terms of a direct sample, i.e. standard kilogram. All others are defined in a way that requires conversion from the measured units to current, distance, intensity, etc. That's because we can get better precision and accuracy that way. So, unless you are measuring mass, you are doing a formula conversion of some kind, already, even if you are just measuring one of the seven fundamental quantities. All other quantities are measured by combining dimensionless constants with the seven fundamentals. Your car's speedometer is a good example. There are no standards for miles per hour. There are standards for distance and time. We can express speed as a function of distance and time, which are fundamental, and thus calibrate a speedometer. We know speed as accurately as we know time and distance. Similarly, we can express pressure as a function of chamber OD and ID (fundamental quantities), dimensionless constants from the physical properties of steel, applied bridge voltage (derived from current x time = charge, and distance), resistance (derived from current and voltage), gage factor (dimensionless quantity), and amplifier gain (dimensionless quantity). So, we can express the variable of interest (pressure) in terms of dimensionless constants, and quantities we can get. The system is then calibrated, and our calibration is as good as our constants, formula, and fundamental quantities. That's the process NIST lays out. The very counterintuitive truth is that, if you have a lot of variables in the mix, fate actually favors you. The probability of all the variables ending up in an extreme state is very small (Murphy's Law notwithstanding). So, you have to combine the variances of each of the individual variables, to get the variance (SD^2) of the error of the final result. The tested net Effective Resolution of the whole system is a trifle over 400 PSI, according to samples taken and math done by me. I did suggest a couple of changes to the PT system, which they adopted, which should theoretically drive that down to about 250 PSI. I haven't had time to retest after the change. Tailgunner and I were posting at the same time. I think he has given good answers. | |||
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Quote: Quote: From Hired Gun on the Gunsmithing Board within the "SAKO Blow-Up" Thread: Quote: Hey Dutch, 1. I see you have recommended a system that is impossible for the person outside a Lab to get an accurate measurement on the Chamber Wall Thickness and which has no way to possibly Calibrate to a known Standard since SAAMI Test Loads are not available to anyone outside a Certified lab. 2. Next you recommend a Mathmatical Model which has no ability to account for the individual Chamber and Bore characteristics of specific rifles. 3. Then you recommend chronographs as a "useful Pressure Gauge" when they only measure Velocity. And you tell everyone how you are so concerned for their SAFETY by saying " I " put them in danger.  But apparently I've missed the part where your great concern for their SAFETY has not explained that "Hired Gun's" post points out clearly that a device "you recommended" can be misleading and has the potential to get them into Pressure Problems. Show us all where you warned them so I can go take a look at it? Or, just hit the "quote" feature and thus highlight it for me. Surely you covered that so as to protect the Beginners SAFETY. | |||
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Quote: What is so hard about getting a measurement of chamber wall thickness? A pair of dial calipers over the outside gets you four significant digits. Fire a cartridge, and measure the OD at that point, with the same calipers, add .001", and you're within .001", which is about .25%, which translates to an error of plus or minus 150 PSI. You are already accepting PRE errors measured in tens of thousands of PSI. Why are you choking at an error two full orders of magnitude smaller? Quote: Apparently you missed the part about using NIST procedures. Of course, what would NIST know about calibration? Once again, Hot Core fallacies 1.2, 1.4, 2.2, 2.3, 2.4, and 3.2. | |||
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Scott, With regard to your 4 questions, I concur 100% with what "tailgunner" said. I also concur with CDH with regard to the use of strain gages. CDH, I have measured PRE on several of my reloads and it is VERY repeatable. By that I mean these reloads produce the same PRE every time within my limitations of making measurements with a 0.0001" increment micrometer, which means ~ 0.0002" repeatability. That equates roughly to 5000 psi accuracy. The pressure is "estimated" by three dimensional von Mises stress analysis of the barrel tenon at the PRE location. Compared to strain gage measurements, which I would consider good to ~ 1200 psi, the two systems line up fairly well (meaning there is typically significant overlap). I would suspect that I am far more anally retentive than most PRE and strain gage users. I also possess a background which aids me, through my formal education, in understanding the output of the rifle system. I have noticed that much published load data errs on the side of caution as much as 5% of a typical pressure trace for a published load (in other words the published data says 60 ksi the pressure traces typically show 57 ksi). I strongly suspect this is done because, since the system is NOT truly calibrated, there is significant potential for error (at least 5% worth) in the measurement system. In my experience it takes considerable and CAREFUL set-up to achieve 0.02% accuracy of full scale, heck that statement is true for 0.1% most times. ASS_CLOWN | |||
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Quote: My results were more pessimistic, but similar. I estimated PRE random error at a standard deviation of 6,800 PSI. | |||
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Denton, I could go look up in my notes the exact "accuracy" of the PRE data. What I did learn though is that the PRE method typically captured the strain gage measurement. With a "net" (5 to 6.8 ksi and I may have been closer to 7 ksi cannot remember for sure too many numbers get sent through my head on a routine basis anymore, or is it just old age?) that big that should not be surprising. It takes a great deal of expertise to turn a PRE measurement into a psi estimation though, and that level of expertise is most likely above and beyond what most reloader are capable of (or willing to do for that matter). Really the approach is the same used for turning microstrains into psi. The "strain gage" in PRE is a brass case, which ain't anywhere near as sensitive as a modern electronic strain gage. Party on you guys! ASS_CLOWN | |||
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Quote: AC could it be the published pressures are max PSI not average? The data could be based on the max allowed pressure although the true average pressure is a couple KPSI lower. The pressure limits set by SAAMI have a average value and a max value. The average can be very close or quite a bit under the max depending on how consistant the loading. Just because the data in the manual states 60000psi if the avg pressure with the given load is 57000psi I would lean in the direction of them publishing the load as haveing the max value if it did in fact show a max pressure at some point in testing. This will have you finding a pressure of 57000psi when in fact the true max pressure very well might be 60000psi and you just haven`t found it yet. Then too they know we all love lawyers..........  As a example the Any Shot You Want manual by A-Square has the 257 Weatherby listed as having a maximum Average allowable pressure of 63861 piezo psi with a maximum individual pressure of 73440 psi piezo Agreed the data for the cartridge example is one on the high side, most show a ~+1600psi (my estimate)variance but it does high lite my point well. The more usual ~+1600 psi max differance from average also can very easily be missed with the admited 5000psi tolerance you believe you are holding with PRE. | |||
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Quote:Hey CDH, From the "tone" of your post, it appears you are a person who can "discuss" this issue without "arguing" about it. It will be nice to discuss it with you. Quote:What would you use to "Calibrate" a HSGS with? Quote:I agree. The question comes up though as "What Pressure?" is the HSGS set-up too? Since the HSGS gives it's readings in Pressure, it is necessary to Calibrate it with a "known pressure". Here I'm speaking for the average person at home who does not have access to Lab Instruments. And of course the PRE Method is simply doing an Expansion "Comparison" to a factory cartridge where the first-hand "result" of the Pressure is measured. Not some second-hand reading from a strain gauge. Of course, the millions of dollars of factory Test Equipment has established their load as SAFE. Knowing what the actual Pressure is, is irrelevant to the excellent and totally repeatable PRE Method. Quote: Surely you do not seriously mean that. Manufacturing companies that buy precision metal parts from outside sources, or that create their own internally, use Micrometers all the time to verify dimensions. They most certainly have to be sensitive and repeatable, or the parts would never move anywhere except to the Scrap Account.Quote:I realize you perhaps have not read all the Threads on this Board about this subject. We have gone over this many times in the past and the thing you are missing is the spirit, or intent of the post to arouse discussion and bring out a few people who just can't talk about things in a civilized manner. As you can easily see, that has been accomplished.  And just like DJ you left out very Best. Quote:I can also agree that. A device capable of reading 0.000,01" is more sensitive and has the potential to be more repeatable to 0.0001" than my regular old 0.0001" capable Micrometers. However, if by "systems" you mean HSGSs, then I disagree because of all the inherent problems associated with the initial set-up and calibration to a known standard. Quote:I can't agree if you are talking about a HSGS. How do you measure accurately the double ogive chamber wall thickness? If this measurement is incorrect or guessed at, what does that say about the data provided by the HSGS? NOTE: For those of you Beginners following this wordy discussion. Go get any one of your rifles and look at the Chamber from all angles. Look at how you can access it to measure it. Then think about how you can accurately measure the double ogive chamber wall thickness with the measurement devicess) you have access to. Then read what CDH has to say in response and see if it is something you can measure accurately at home. Quote:I'm an EE myself. Concerning electronics I "Trust but Verify" as President Reagan would say. I have no problem at all saying a Redundant Strain Gauge System inside a Certified Lab is an absolutely excellent device. I can see where people reading my posts in this thread would get the impression that I don't think they are useful "anywhere". But, if anyone is interested in wasting time doing a search, they can find I've always said Strain Gauge Systems should be used in Certified Labs. This is because they will have access to equipment which can accurately measure that double ogive chamber wall thickness without guessing. And they can also get SAAMI Calibration Ammo so the SGS can be verified to a "known Standard". --- Quote:One of the most interesting lectures I've ever been priviledged to hear was from an old ME, Mr. Flint, that had 55 years in a company I worked for. (My boss only had 51 years and Mr. FLint refered to him as "The Rookie"!!! )Mr. Flint gave me a 30 minute lecture on how a "Tapered Drift Pin" was intended to work. The Company had not used them for at least 25 years, but his words were absolutely mesmerizing. Extremely clear and well thought out when he told me the history of their use in the "old" product line. | |||
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Quote:Hey AC, Any chance you ordered the 55gal drum of Mylanta for the HSGS worshipers? Quote:Or more when the set-up dimensions are "guessed at". Pitiful!!! | |||
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Hot Core, care to estimate the real world probability of a read error using a micrometer, vs a read error from a chronograph? Dutch. | |||
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Quote: You have been arguing all this time without knowing where strain gages are actually applied, in the middle of the case. There is no "double ogive" there, just a straight linear taper. That's the funniest thing I've seen all day. Hot Core doesn't have a clue how strain gage systems are actually used. | |||
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Quote: A micrometer is a fine and repeatable instrument, and will give you the dimensions of brass, or other material. The dimensions of brass do not repeatably indicate pressure. PRE has poor repeatability. By Hot Core's logic, I should be able to monitor the air/fuel ratio in my car by miking the tailpipe, and keeping track of changes in diameter, because the micrometer is very accurate and repeatable. | |||
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Quote: Then you should be able to answer a few extremely simple EE questions for us. Please demonstrate your knowledge by posting your answers here. I guarantee that this is all extremely basic stuff. Anybody who is really an EE, and who is old enough to have "20 years experience with strain gages" can give all the answers immediately, without having to use references. 1. A linear voltage "ramp" with slope 10 volts/sec is applied across a .01 microfarad capacitor. What current flows through the capacitor? What is the waveform of this current? If you don't want to do the math, just give the formula. 2. Why are strain gage outputs traditionally taken across a Wheatstone bridge, and fed to a differential amplifier, rather than using the simpler voltage divider method, feeding a single input amplifier? 3. What does CMRR stand for? Define or explain the term. 4. In a common emmitter class A bipolar transistor amplifier, why might the designer opt for emitter degeneration? How is this done? What are its effects? 5. What are the unique advantages of the cascode circuit topology? 6. Two identical strain gages with resting resistance 350 ohms and gage factor 2.1 are connected in series, and applied to the same barrel, at the same distance from the receiver, where the barrel is 1.2" in diameter. 10 volts are applied to the series string of gages. A cartridge is fired from the barrel, creating 500 microstrains at the surface of the barrel. How much does the voltage at the junction of the two gages change? 7. A real softball: What does a strain gage look like? Come on Hot Core, show us the "EE" isn't just another fabrication. | |||
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Quote:Hey Dutch, Where was that you warned all the folks you are worried about? | |||
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Hot Core believes that because a micrometer is an accurate and repeatable device, then, since PRE uses a micrometer, it must follow that PRE is an accurate and repeatable method of estimating pressure. News flash: Chronographs are highly accurate and repeatable devices, too. Since muzzle speed is related to pressure, and since chronographs are accurate and repeatable, doesn't Hot Core's logic say that chronographs are an ideal instrument for estimating pressure? | |||
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Quote: Like I said, you suggest using factory ammo as the 'standard' to calibrate/verify your results. The same technique works with a strain gauge system. It does not matter how badly you measure the chamber wall dimensions...forget for a moment the actual numbers the SG system gives and just empirically compare the curves with factory ammo, if your 'test' rounds give lower peaks, you can trust with high confidence that your ammo has a lower peak pressure! How is that scenario different from: Quote: And of course... Quote: ...I have read and even been involved in some. My conclusions, and yes, they are only my own, YMMV, are that PRE is useful for a rough estimate, 5000+ PSI or more depending on how good/bad one is with a mic. Even is all the SG proponents are reducing their estimates by half, SG technology is good to 1000 PSI resolution. ...and I am not trying to pick a fight, but Quote: Strikes me as a singularly poor motivation to post.  Have fun guys, my mind is made up!  | |||
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CDH, Quote: In many cases I doubt it is even that good. The resolution of the strain gage system is SIGNIFICANTLY effected by the barrel wall thickness and the actual diameters of chamber and barrel tenon OD at the location of the strain measurement. <this statement is true for pressure measurements ONLY> With regard to relativity (pressure curve of one load versus another). I would agree that the Strain Gage system is MUCH more resolute than the PRE system. Again we are speaking ONLY about RELATIVE, NOT ACTUAL pressures!! ASS_CLOWN | |||
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Hot Core, the best thing to do is to follow Ol' Joe's advice, and quit digging. You're not really an EE, and everybody knows it. If I'm wrong, answer the questions, and show the world. I challenged InfoSponge once, and he nailed all of my questions instantly. I gladly posted to the world that his credentials were genuine. $3,750 for a strain gage setup?? What planet are you on? $650 for a basic laptop, and $200 for the PressureTrace, or, at one time, $189 for the Fabrique unit, which requires no laptop. Yet another incredible fabrication, trying to defend an indefensible position. Are you perhaps spontaneously channeling Bahgdad Bob? The combinations of pressure and velocities you posted in your example are physically impossible. Why would anyone try to justify or explain something so ridiculous? Just for grins, try explaining how SAAMI standard ammunition gets calibrated. There is no NIST pressure standard artifact for SAAMI to compare with. Since, according to Hot Core, you can only calibrate by directly comparing with a standard in the same units, and since there is no available pressure standard artifact, according to Hot Core, SAAMI can't calibrate that standard ammo. Fortunately, NIST provides a method. And it is the same method home strain gage users apply to calibrate their systems. | |||
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Quote: Can we agree that some assumptions have to be made here? Assuming that your data is reasonable, and I think the pressure and velocity spread is too large to be real...actually I think you manufactured data specifically to screw up assumptions (high pressure-low vel, low P-High vel, etc) Forget about velocity data...too many variables like barrel length that are totally irrevelant to this discussion Assuming that the factory ammo is loaded to safe pressure (and one really needs multiple loads from multiple lots and manufacturers...3 is sufficient, 5 is better) Each user has established a reasonable max PRESSURE READING (not actual pressure) for their gun. As long as their reloads do not go higher than these readings, they should have a safe load for their gun. Velocity be damned...pressure is the thing we worry about due to safety concerns! And....they have done so with a far lower number of firings (most authorities recommend a very large number of rounds to be averaged for PRE/CHE to get meaningful data) and far higher confidence level. Simple enough? | |||
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Quote: You plug the PressureTrace into the computer's USB port, plug the strain gage into the PT cable for that, and boot the computer. What consumes the other 58.5 minutes? Yet another ridiculous Hot Core fabrication. How do you expect anyone to take anything you say seriously, when you invent a EE for yourself, and make huge exaggerations like this one, and the price of strain gage equipment? | |||
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Well, alright: Quote: 1. None of the loads calibrated the M43. The M43 is calibrated by taking the ID and OD of the chamber at a point about halfway down the casing, where the strain gage is applied, and by applying the standard NIST procedure for indirect calibration. The system is then calibrated within a tolerance. The question for you is, how would you derive a calibration for PRE? How is PRE calibrated? 2. The pressure reading is as accurate as the input variables (ID, OD, amplifier gain, etc.) make it. It can neither be better nor worse than that. If the input variables are good, the accuracy is good. With ordinary dial calipers, and medium grade strain gages, the calibration is within 1,000 PSI for the PressureTrace model. If everything has been done correctly, the pressures accurately represent the peak pressure of that lot of ammunition in those different guns. The question for you is, how good is the calibration for PRE? 3. How will this help them develop loads? If, as you say, they are using commercial ammunition, it provides a sanity check on the calibration previously done. If I got those pressures, I'd worry that I had made a calibration mistake. Standard Super X 30-06 runs about 55 KPSI, with Federal High Energy a little above 58 KPSI. These are so far below that that it is worth double checking the system. The question for you is, since PRE is incapable of reliably detecting 10,000 PSI differences, how would PRE give you any idea at all that any of this was going on? | |||
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Quote: Quote:Hey CDH, Absolutely. The data for "Bob" is directly from Hodgdon #26, but the others were intentionally skewed by me slightly to represent what can potentially happen with different rifles. I did not skew it to "screw up assumptions", but to represent what I figured to be a typical Pressure spread amongst 5 different rifles using the same Load. If you believe the spread is too much for 5 different rifles, how much could we realistically expect the Pressure to fluctuate from "Bob"? You base this information on your experience with "How many?" rifles chambered for the same cartridge? Not trying to put you on the spot, just trying to get an idea how well exposed to multiple rifles in the same cartridge you are. For example, I've had 6 different 30-06s over the years and I believe 12 different 308Wins. And of course, multiples of other calibers. Please consider that each person above measured their own chamber "to the best of their ability" with measuring devices available to the average person at home. Isn't there enough variance in those measurements to skew the Pressure that much in 5 different rifles, or variance in the Chambers, or variance in the Bores? Quote:Now, that is news to me that I was unaware of. I've never heard during the (attempted) Calibration of the HSGS to ignore the Velocity. Not a problem with me ignoring it at all. Quote:I had 4 different Factory Loads(actually all out of Hodgdon #26) in my question to start with and really thought everyone would say I was trying to confuse the issue. I'll be glad to repost with those Loads and a few more, if that helps you explain things to me. (Look for it below.) Quote:I'll give the other Pressures and you can better explain it to me. But, so far I like what you are saying and understand(or believe that I do). Quote:I'm not talking about PRE/CHE in any of the above questions. Is this relevant to my questions? Don't take that as smart-mouthed, cause it isn't intended that way at all. I just don't understand why you began discussing PRE/CHE in the context of explaining the HSGS to me. But, I do agree that a Beginner should shoot an entire box of cartridges(20) and "Average" the PRE value, then write it on that box of empty cases so that piece of data can not be lost. That becomes his Comparative Benchmark Standard. --- Here is the additional data. Let's assume it was all taken by Bob using 5 full boxs of each different factory load in his rifle. Below is the "Average PSI Value" for 5-20 round boxs(100 total shots "PSI Average" per listed psi) of each type: 43,400 psi 48,000 psi 47,200 psi 48,700 psi 50,500 psi 49,200 psi 48,400 psi 51,000 psi 50,700 psi 44,100 psi 47,400 psi 49,100 psi 50,000 psi 49,200 psi 49,900 psi 48,900 psi 49,100 psi 44,000 psi 47,500 psi 49,400 psi Those are all straight out of Hodgdon #26 for a 150gr 30-06 and could potentially be Factory Ammo which could be purchased across the counter. No "Velocity" given per your request. So, how any does the above data assist in the "Calibration" of the M43? Thanks CDH for helping me gain insight into this issue. I sure didn't know about "ignoring" the Velocity during the (attempted) Calibration. | |||
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Quote: It doesn't. There is no reason that it should. Strain gage calibration is not accomplished by comparing with factory ammo. | |||
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OK, time's up on the quiz. Hot Core has had a couple of days to show that he is a real EE. He's not. Quote: Answers, for those dying of curiousity, and just so everybody knows they are real questions. 1. C dv/dt. The current will be simple DC. 2. So that noise picked up by the device leads will appear simultaneously at both inputs of the differential amplifier, and will be suppressed. 3. Common mode rejection ratio. It describes the ability of a differential amplifier to reject a signal that appears on both its inputs. 4. It is accomplished by adding unbypassed resistance in series with the emitter. It reduces noise, increases bandwidth, and raises input impedance at the expense of low frequency gain. 5. High input impedance, excellent bandwidth. 6. If they are identical, and subject to the same strain, the voltage at the junction will not change, regardless. This is one component more complex than the simplest possible circuit, and a total no-brainer. 7. The really easy softball: A strain gage is about as thick as heavy paper, and about 1/4" square. So, as far as I can tell, Hot Core fabricated his EE credential. | |||
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Hot Core, You have visions of adequacy! HogWild | |||
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All, A little food for thought. Lets consider two rifles. Rifle number one is a 416 Rigby with a 1.2500" OD barrel shank. The chamber diameter below the strain gage is 0.5650". The barrel expansion at 50,000 psi is 0.00074" Rifle number two is a 30-06 with a 1.2500" OD barrel shank. The chamber diameter below the strain gage is 0.4560". The barrel expansion at 50,0000 psi is 0.00044". Now if there are errors in the chamber and barrel shank diameters. For rifle number one the chamber is erroneously measured to be 0.566" (0.001" too big), the shank is erroneoulsy measured to be 1.2510" (again 0.001" too big). The barrel expansion at 50,000 psi is 0.00075". That amounts to a 1.35% error in pressure for rifle number one when compared to the CORRECTLY measured barrel [(0.00075-0.00074)/0.00074]*100% , or 675 psi (at 50ksi actual) For rifle number two the chamber is erroneously measured to be 0.4570" (0.001" too big) and the shank is correctly measured at 1.2500". The barrel expansion at 50,000 psi is 0.00045" That amounts to a 2.27% error in pressure for rifle number two when compared to the CORRECTLY measured barrel [(0.00045-0.00044)/0.00044]*100%, or 1135 psi (at 50ksi actual). The reason that barrel one has less error than barrel two is the sensitivity of the systems. Simply put barrel one is less stiff than barrel two so it gives more. The strain gage is simply measuring give in the barrel. Now none of what I have just posted has ANYTHING to do with the +/- 0.4% error of the gage (or thereabouts) or the +/- 0.4% error of the electronics (or thereabouts). When you consider the fact that many labs may have electonics that are only good to 0.75% to 1% and will use the cheap +/- 1% strain gages, it is very believable that there could be a 4% to 5% error in recorded pressure. I have seen this level of error in several published load manual loads. The error I posted is due simply to the combination of system stiffness and inaccuracy in measurements. This error will exist with any system which has not been discreetly calibrated. The Oehler or any of the other strain systems for that matter, solve for psi just like I did. They take the inputed barrel dimensions, the material properties of steel, etc, and perform a strain/stress calculation and determine internal pressure. Now you gentlemen argue on all you want. ASS_CLOWN | |||
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AC-Nice job of outlining a possible high end error scenario. I am tired of this discussion and the endless "but...but...but...what about...what about" No sign of intelligent life here, beam me up Scotty! | |||
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AC, I think that's generally a pretty good analysis. There are only a couple of places we diverge. The amplifier accuracy is much better than that. Modern instrumentation amplifier chips are flat amazing. Their gain is extremely precisely and accurately determined by a single external resistor. Getting resistance to .1% and 50 ppm/degree C or better is easy, and the amplifier follows. There is no reason to assume 1% strain gages, when .5% is what's actually in use. The other issue is that tolerances do not simply linearly add. You have to stack them up with a square root of the sum of the squares approach (root sum squares). So, if your dimensions are a little off, and that error has an SD of .5% (-1.5% to +1.5% at the three sigma points), and your gage is a little off, with an SD of .25%, the net SD of the error is .559%, not .75%. The error distribution will be almost completely determined by the largest single source. Given that, from your math, my conclusion is that the system is good to within a couple of percent, or about 1,000 PSI... maybe a little worse in some cases. Suppose it is twice that. That is still an adequate system, considering the random error in the commercial piezo system prevents you from reliably getting closer than 850 PSI in a ten-shot average. I assume you mistyped your bore diameter, and that your calculations were actually correct? | |||
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Quote: Hot Core, when you make shit up you pretty much loose all credibility in this arguement. If you have facts to support an arguement your opinion is valid, if not you're just wasting our time. Please just be honest......DJ | |||
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Quote: ass clown I`m not arguing that a percentage of the listed pressure in the manuals is or isn`t in err but, I`d like to know where or when and how you`ve tested the loads that showed you the error? To say err of this size is possible I`ll buy, but to say you`ve found the err exists I`ll have to question.  There is tolerance built in pressure ratings with a high and a low acceptible limit. The same as in every manufactured good and apparently as you point out in lab equipment also.The variation you might find could be normal variation in pressures with the tested load or maybe a product of the err in both the labs and your equipment. A quick look at the Hodgdon manual shows pressure in psi values listed at a figure rounded off to the nearest hundredth. The SAAMI pressures are a average, and have max allowed max. I`m sure the manuals writers work towards a average thats as close to the SAAMI figure as possible with out exceding the max and listing the result. I`d also bet they avg more then 10 or 20 rds to reach these numbers. Hodgdon, I`ve been lead to believe, uses powders that fall dead in the middle of the accepted burn range for that propellent when working up their data. Depending on the direction your can of powder varies from the norm you`ll surely find a bit of error. The fact you only find a 4% variation from their listed pressures is amazing when you take the variations in test bed, equipment, components, possible temp, the rounding of the numbers, and the procedures followed to arrive at a conclusion. I don`t think the argument here is whether or not err exists in strain gage systems but if one can give a acceptably accurate relation to a standard no one can apparently show a exact value of. | |||
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Quote:Hey DJ, I told everyone I had "made-up" the numbers, otherwise no one would have known they were "made-up".Quote: Were else could I have gotten them since I don't have that information available? So you are attempting to chastize me for using fictious data in a fictious example intended as a question so I could understand from CDH how that issue would be addressed. How should the fictious question have been structured to remain credible? And please feel free to answer it once you show me what I should have asked. --- Hey CDH, I really don't understand: Quote:You said I needed to include more Test Results which I did. They all came straight out of Hodgdon #26 and none are made up. So, once I did as you asked, you consider it "endless questions"? --- I think I now understand: 1. The chamber thickness must be guessed at by the HSGS user, but that is OK because putting "wrong data" into the HSGS doesn't affect the outcome that much. 2. Calibration is done by repetitive testing with an "unknown Pressure", but that is OK. 3. You can't use one box of cartridges, but if more are used that is considered an endless stream of confusion. 4. If you ask simple questions about how the set-up is done and the HSGS Calibrated, then those questions are met with ridicule. And if you alter the questions to please the person you are trying to get the information from, then that is an "endless questions"? 5. If you do not have First-Hand data to use in a fictious question, it is improper to create some variance in a fictious example. Really appreciate all the sincere replies to the questions I had. I now realize you all consider the HSGS an excellent piece of equipment as long as you do not have to answer any questions about it. That seems to bring us full circle to: HSGS = Reloaders Pyrite (aka Fool's Gold) | |||
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Quote:Excellent! | |||
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Quote: Measuring to within .001" is not guessing. However, the strain gage system is much more robust to small errors than PRE. How do you expect anyone to take anything you say seriously, when you exaggerate like this? Quote: No, it is not. How do you expect anyone to take anything you say seriously when you exaggerate this way? Quote: Illogical and irrelevant. How can you expect anyone to take anything you say seriously when you exaggerate this way? Quote: How can you expect anyone to take anything you say seriously when you twist the facts like this? Quote: How can you expect anyone to take anything you say seriously when you twist the facts like this? Quote: No you're not. How can you expect anyone to take anything you say seriously, when you fabricate credentials for yourself? | |||
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Hot Core, I will give you credit for telling about the fictitious examples. But when you are using a hypothetical you should more clearly denote it. As far as your example itself it's kind of like the following hypothetical: A three legged alien from Zarnak gives you Data A An Honest Bill Clinton gives you Data B A voluptuous Blond who wants to have sex with you gives you Data C Which Data is relavant and could be used? . . . . . . . . . The answer is none of the above since none of the above exits! .......DJ | |||
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Here is a question that will probably reveal how naive I am: why can't you drill, tap, and weld a pressure fitting somewhere on the barrel (around the chamber) and then attached a peak reading pressure guage? How stupid is that? Kory | |||
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What you are describing is similar to a SAAMI style pressure barrel that is used by many of the larger bullet, powder and ammunition laboratories. The pressure is measured by a piezo electic transducer. Call HS Precision. They make those. JCN | |||
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The largest source of error has been ignored so far. The relationship between strain (measured) and stress (what is wanted) assumes a long, uniform cylinder. One end of the barrel is reinforced by the breech, the bore is tapered, and the end of the chamber is reinforced by the taper of the shoulder (thicker). The gage is mounted less than a diameter away from these points. According to Vaughn's "Accuracy Facts" when a strain measurement is compared to a calibration (hydraulic) it reads 20% low (as in ouch). In a correspondance with OKShooter he told me that the maker of the electronics puts in a correction (fudge factor) to account for the error. That is why a commercial load is used as a bench mark. The electronics (resistors, gage, power source, amplifier gain, ect) are probably accurate to a few percent, what they are measuring is the question. Good luck! | |||
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Quote: 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: 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. | |||
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The Accurate Reloading Forums THE ACCURATE RELOADING.COM FORUMS Guns, Politics, Gunsmithing & Reloading Reloading Re: How do I figure out pressures?
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