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:Hey HogWild, First off let me say I did not intentionally reverse your handle. I know you didn't mention it, but I just caught it and want to correct myself.Quote: What you are missing is that I'm interested in your opinion not a quote from someone else. I would think you have some first-hand experience or education which applies to the HSGS, or you wouldn't have joined in this discussion. So, tell me what you know from your experience and education to help me understand "why" you think so highly of a HSGS. I realize you have not been on this Board long enough to have seen some of the previous dis.. arguments concerning HSGS devices. A long time ago I said I would no longer respond to one particular poster who I've just lost respect for. That person is totally unable to "discuss" the issue in a rational way. So, you have now quoted two sources that don't help your position "from my view". If they are your only source of knowledge concerning the HSGS, then I wish you the very best of luck and hope they don't get you blown-up. Quote:I'd be interested in knowing which statements you consider insane. But please explain "why" they appear to be insane from your view. I certainly do not think of you as a fool (yet  ). | ||
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Quote: All of the following: 1. Standard list of Hot Core fabrications, unsupported by any known facts or credible references, all posted by Hot Core for everyone to see--- 1.1. Mounting a strain gage on a rifle will spoil the accuracy. 1.2. You need a CMM to measure the ID and OD of a chamber. 1.3. Mounting a strain gage will rust your rifle. 1.4. Strain gage systems cannot be calibrated, and the results are just a guess. 1.5. PRE is completely repeatable and reliable. 1.6. PRE is calibrated. 1.7. Claims to have 20 years of experience with strain gages. 1.8. Claims that strain gages don�t work outside a laboratory. 1.9 Quotes Ken Waters, the �father� of PRE to support his claims, when, in fact, Waters contradicts Hot Core. 1.10 Claims that a laptop computer and a $200 PressureTrace unit cost $3,750. 1.11 Claims that it takes about an hour to plug the PressureTrace into the computer, connect to the strain gage, and boot the computer. 1.12 Claims that measuring chamber dimensions with a dial caliper is just a guess at the dimensions. 1.13 Claims that the one and only way to calibrate anything is by direct comparison with a known artifact in the same units of measure. Can't explain how you calibrate an automobile speedometer using this method. 2. Standard list of Hot Core self-contradictions� 2.1. Claims that you can use factory ammunition as a maximum pressure reference. Also claims that you cannot. 2.2. Claims that you need SAAMI standard ammunition to calibrate a strain gage, but that you don�t need it to calibrate PRE. 2.3. Claims that you cannot use chamber dimensions to calibrate a strain gage, but that you can use brass dimensions to calibrate PRE. 2.4. Claims that he gets four significant digits measuring brass with a micrometer, but the rest of us can�t get three when measuring a chamber. 2.5 Claims to be an EE, but can�t answer simple questions about analog electronic circuits. 2.6 Claims that PRE is calibrated, and accurate. Also claims that it is not, and that knowing actual pressure is irrelevant. 3. Hot Core logical fallacies/half truths-- 3.1 Hot Core can teach anyone to use a micrometer in five minutes, and it is a precise instrument. Since it is a precision instrument, and easy to use, it follows that the dimensions of a brass casing accurately and precisely reflect the pressure of a load. 3.2 Refuses/fails to provide any credible references or experimental data to support his assertions. 3.3 Argues that it is impossible to get adequately accurate chamber dimensions, because they involve a �double ogive�. Obviously does not know where strain gages are actually applied, on the outside of the chamber over the middle of the cartridge case, and that the only chamber measurements needed are a single ID and OD. Quote: Carefully done experiments, structured according to the best industry practices, show that the system is highly linear and repeatable, i.e., will routinely give the same answer in response to the same pressure. A theoretical model, built on NIST standards, indicates that it has very respectable absolute calibration. There is nothing more to expect of a measurement system. The question for Hot Core is, what, in your actual experience with rifle mounted strain gage systems, indicates that they do not perform as stated? Here's an offer for you, Hot Core. All the items on the standard list are directly from you. If you've changed your mind about any of them, let me know, and I'll take them off the list. | |||
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forgive my guessing but are you trying to rebarrel a M-1 Garand?.....if the answer is yes then just do it and start reloading the new barrel's chamber with minimum reloads and "up" the powder a little at a time until the mechanism is functioning correctly and consistantly.....assuming that you not exceed the published maximum loads. | |||
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Measuring brass or looking at primers will tell your operating pressure within about 20,000 PSI. For a quantitative analysis, see the current issue of Varmint Hunter magazine (the article is by forum member Denton). A manual will tell you much more than that, and a chronograph more, yet. By a factor of about 4. JMO, Dutch. | |||
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djpaintles, You and the other strain gage proponents would you mind answering a question for me? How accurate is an uncalibrated strain gage system? Seriously, just how accurate is the resistance or potential output of the strain gage being used? By the way, I already know the answer to my question, I work with strain gages all the time. They are much more accurate when used with a calibration curve. Problem is even "calibrated" ammunition isn't all that pressure precise, so to speak. We won't even get into the issues with barrel measurements that need to be done for a do-it-yourselfer at home. I assume the ballistic labs know how measure theirs, but I also know that they know there is a significant error in their pressure measurements (albeit not as bad as with PRE). I really think you guys are fooling yourselves. Pressure load data from "Any Shot You Want" 6.5-06 (26" barrel) 140 grain Sierra IMR7828 52 grain for 37900 CUP and 2631 fps 55 grains for 44700 CUP and 2833 56.5 grains for 49200 and 2941 Rl 22 50 grains for 34300 CUP and 2554 55 grains for 46800 CUP and 2907 56.5 grains for 50400 CUP and 2954 100gr Nosler Ballistic Tip H4831 55 grains for 35800 CUP and 2934 60 grains for 47300 CUP and 3278 IMR7828 56 grains for 34400 CUP and 2919 61 grains for 46400 CUP and 3312 Max pressure is 53000 CUP (30-06 is 50000 CUP) 280 Remington (26" barrel) 140 grain Sierra BT Rl 15 46 grains for 42000 CUP and 2820 50 grains for 49300 CUP and 3006 I would opt for the fastest appropriate powder. Hope that helps you out a bit. ASS_CLOWN | |||
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No manual,quickload program,chronograph or pressure ring measurement is going to give you an "accurate" pressure measurement for a given load in your rifle with your components.They will give you estimations that may or may not be in the ball park but they will never provide an accurate value.Unfortunately they are all that the average reloader has at his disposal so we must make do with what we have.I personally look for pressure signs such as excessive case expansion at the web,shiny spots on the case head and sticky extraction after firing because they are the best indicators that I have at my disposal.I also look at chronographed velocities but I do not pretend that any of these methods are truly accurate methods of pressure measurement.They have however prevented me from experiencing any damage to myself or to my guns and have resulted in good case life. | |||
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I totally agree with Dutch, a chronograph is the best most accurate pressure indicator that most average reloaders have. Since you want to figure a relative pressure I would use a Chronograph and quickload if you can't get access to an Oehler 43 or something. I would use quickload to guesstimate the pressures by varying the powder charge you're using in the 30-06 until I matched the actual velocities you get from your rifle. Then with the new barrel I would vary the powder charge in the new caliber until I matched the pressure. Quickload is of course a computed estimate but I feel that it's relatively accurate as far as pressure when my powder, bullet and barrel length match the velocity estimated. This is a little hard to explain, but if you play with Quickload you'll see what I'm getting at.........DJ | |||
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Alf, Excellent post! You most certainly are ignorant about reloading and internal ballistics.  ASS_CLOWN | |||
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Hot Core, Reading pressure in firearms can be as much an art as a science. Every method that we have at our disposal has significant disadvantages. A prudent reloader will use as many different indications at his disposal while recognizing the disadvantages of each. Saying the one method is completely superior to others is simply wrong. The Copper Crusher Method is useful in only the test chamber since it has to be specially modified to perform this test. Accuracy is also limited buy the measurements of the crushed cylinder and the accuracy of the charts themselves. The Pzeio Electric transducers used by the hobbyist reloader is limited by not having a reference round to calibrate the system. It will however within the same rifle give an accurate difference of pressure between 2 rounds tested. So while not able to give a truly accurate absolute pressure it will give accurate relative pressures. The Pressure Ring measurement is limited by many factors. What is the reference pressure? It can't give accurate readings of absolute pressures and can only give relative differences between different loadings. It is also limited by differences in brass construction and composition and can be difficult to measure consistently. I've read at least 4 different recommendations on exactly where the measurements should be taken. Variations in chambers, brass etc. make this a useful tool but one that needs to be understood within it's limitations. The Chronograph is also a useful tool. If you are getting consistently higher velocities that the standard loads you are loading to higher pressure. The chronograph is of course less useful when standards aren't well established as in wildcats. Bolt lift, flattened primers, ejector marks while definitely signs to back off of can also be misleading. I've seen several loads that when fired in carefully blueprinted action showed no difficulty in bolt lift whatsoever but nearly required a hammer to open in a rifle with less lug contact etc.. Just how flat is a given primer? Different cups of differing thicknesses and hardness can give different indications with the same pressure. I've seen rifle's with rough bolt faces that would leave ejector marks on light loads. Computer programs will give estimated pressures that are totally accurate only if your chamber is truly a perfect cylinder, your bore is exactly to a nominal spec etc.. Again a useful tool but vulnerable to inaccuracy if there are variables that the program input can't account for. So the best method for determining pressures is a combination of all of the above. No single method can be completely relied upon to give an accurate absolute pressure. We as hobbyist's won't have access to all of the given tools but we can cross check our findings with manuals and other sources that have performed tests that we might not have access to. I don't believe that there is such a thing as a Miracle load that for some reason allows a given reloader to suddenly obtain 200fps faster at a normal pressure than everyone else .......DJ | |||
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When reloading for the Garand, it is important to use a fairly fast powder such as 4895 or 4064. The use of a slow powder such as H4831 changes the pressure curve so that when the bullet passes the gas port, pressure is still very high. This is very hard on the op rod as the higher pressure causes the action to cycle violently. This violent cycling can happen even though muzzle velocity is the same with both powders, and peak pressure will actually be lower with the slower powder. When you change to a smaller bore with its associated expansion ratio, it will be difficult to maintain the pressure curve for which this rifle was designed. Hopefully a gunsmith who is very experienced with the Garand can guide you in the right direction by porting the new barrel properly for the cartridge you decide to use. I know several guys who shoot tricked out Garands competitively, I will see if I can get you a contact for a reputable gunsmith with experience on this weapon. | |||
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Quote: Within .5%, for the mid-grade gages, according to the manufacturer. | |||
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Idaho- If you could give me a heads up for a gunsmith that might be willing to take on this challange of making a garand into a 6.5-06 it would be greatly appreciated. And thanks again to everyone whos had input so far, lets keep it coming. -Scott | |||
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Scott you have mail One other thing to consider is a adjustable gas plug, which modifies the venting of the gas chamber (work up a accurate load with the vent wide open, than close the vent down a little at a time until the action cycles reliably). Gas port pressures & powder burn rate become a lot less critical this way, without endangering the op-rod. | |||
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Scott Programs gives you a ballpark figure, for the individual rifle you must test each load. The Kolbe P-Max model CP-1 is really handy to use, costs approx. 250�. http://www.border-barrels.com/p-max/p-max-3.htm Cheers / JOHAN | ||
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Quote:Hey DJ, Noooo, not "The Best of all Time?", the very best of all time.Quote: Quote:I really hate to say this, but wrong again. PRE is extremely reliable and has been so for more than 100 years. The reason the Powder and Bullet Manufacturers have gone to Strain Gauges in their Ballistic Labs is because of time constraints, record keeping, cost compared to CUP measuring devices and the Labs ability to obtain SAAMI Certified Reference Ammo(something the HSGS user can not get) so they can actually Calibrate the system to a Standard. Quote:DJ, you did well with that logic, especially since it is the "very best Pressure Detection Method of ALL TIME!!! Quote:Surely you are now talking about HSGS. | |||
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Hotcore, I have no problem with you defending your pet method, but posting the kind of bizarre, unfounded crap like above is going to hurt someone, sooner or later. Measure all the cases you want to, but I take personal offense to you putting fellow reloaders in danger by suggesting that measuring changes in case size does anything but tell you case growth. If this method is so reliable, why, then, do case thickness, brass composition, chamber size, powder burn rate have more correlation to brass size changes than pressure? JMO, Dutch. | |||
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Denton, Who's gages are you using? ASS_CLOWN | |||
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Quote:Hey Dutch, I feel the same way about chronographs and HSGSs that you do about the very best (and completely SAFE) Pressure Detection Method ever devised - PRE. Quote:I feel the same way about people recommending chronographs and HSGSs without "Warning" folks that they can be extremely misleading. Those of you who believe a chronograph is God's Gift to Reloaders might find a particular Thread on the Gunsmithing Board interesting. There is a Thread currently active about a "SAKO Blow-Up". Within the Thread, a new to this Forum guy joins in and mentions he nearly blew himself up using a chronograph to determine when he had reached MAX by just continuing to keep dumping in Powder in order to reach some randomly picked, arbitrary Velocity. He was not using a SAKO. I would encourage anyone who is in anyway interested in Pressure Indicators to go read that Thread. When you get to his post, read it and let it sink in. Then think about where you were warned over and over on this Board about how a chronograph "has the potential" to get a person in trouble with Pressure. (Your Welcome!) Quote:Let's break it down: 1. Yes PRE is reliable, repeatable and totally SAFE by anyone who cares to try it. 2. "The results of" the Thickness, composition, chamber size and Powder Burn Rate all go into determining the Pressure Indications which can be detected with the PRE Method. 3. The "correlation to brass size changes" is what makes it SAFE when done properly. You simply compare your Reload's PRE to a Factory PRE and when they are the same - STOP. | |||
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Quote: So today you're saying that factory ammo is a satisfactory standard of comparison? Just checking to see which side of the fence you are on at the moment. That would be Hot Core self-contradiction 2.1 and 2.2 again. Quote: http://www.shootingsoftware.com/ftp/dbramwell%20july%2019%2004.pdf Take the challenge on page 7. Do your own test--it's very simple. Be guided by what the data tell you. | |||
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Quote: MicroMeasurements, out of Raleigh, NC. Sealed, and temperature compensated to steel. $10 each. PIA to do business with. | |||
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Denton, I enjoyed your article. I printed it out to save for possible use later. If I do the experiment I'll give you my results to add to yours. When you were measuring did you always measure the largest part of the case. When I've measured both PRE and CHE I've often found the cases to be out of round enough to exceed the tolerance of the measurement itself. I guess that I would disagree somewhat with your RIP conclusion because I think that it can be a useful test to double check others. I guess that I'm skeptical of all the types of measurement so I'm not willing to accept one as the be all and end all. My reloading strategy is compare as many manuals and data sources possible and see if there is any trend towards a couple powders most suitable. I then try and load to the velocity that seems to be the most common top value (I discount any sources that list very low or high figures). I'll measure case heads, make sure that primer pockets stay tight, look for flattened primers, and make sure I'm not getting abnormally high velocities. If a load is accurate, doesn't show any of the normal pressure signs, has a normal velocity, and isn't over what the different manuals suggest......It MIGHT be OK.............DJ | |||
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When you were measuring did you always measure the largest part of the case. Yes, but... Per the original Waters article, I would twirl the case inside the micrometer, looking for the "high spot". But you can have more than one high spot, and that adds to the non-repeatability. Using the electronic blade micrometer, and measuring the exact same spot on the same case over and over, the Effective Resolution was .00005", just like the micrometer specs say. Twirling the case reduced the Effective Resolution to .00017", so it's good to a couple of tenths, which is not very small compared with the .0005" CHE that the books say should worry you. I don't find any fault with your approach. There is a lot of random measurement error in the loading manuals, which is why no two of them agree. Tossing the outliers, and taking a middle value is very prudent. If people want to measure cases, I don't have any problem with that, either, as long as they understand the magnitude of the random error, and use the information accordingly. A measurement system loaded with random error can still be intelligently used. The problem is, most people don't understand that limitation, and so expose themselves to danger. As you can see from the graphs, I had 60 KPSI cases that showed no growth... so, guys that don't understand what's going on think they are OK, and run their 243's up to 70 KPSI, wanting desperately to believe that there is something special about their gun that safely gives them an extra 150 fps. And, anyway, the SAAMI specs are not designed to take you to the threshold of catastrophic failure. They are simply an economic operating point, where barrels and brass give good results and last a reasonable number of uses. Running your 243 at 70 KPSI has a low probability of killing you. Most often, it will just wear your gun out a far faster, and ruin your brass after 1-2 reloads. Glad you enjoyed the article. If you do the experiment, please be sure to post the results, however they come out. | |||
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Quote: Hot Core is this the post you`re refering to? Quote: Condeming a method because of someones failure to notice (pay attention to) his equipments obvious error reading(s) is not the way to prove your point. I use PRE and have for a long time. I also use a crono, primer apperance, bolt lift, and data from a newer print date manuals to "estimate" if my results are with in a safe range or not. The fact the reading on his crony quit changeing with powder increases or were in the wrong vel range to begin with should have raised flags. I`m sure if you drop or otherwise bump your Mic you check the calibration against a machinists standards block? I`m also sure you can measure accuratly every time to four decimal points with out error? If you fire a given load today, measure and record it, reload the case with the same load, components and equipment, and fire it next week will it always show the same PRE? I`m not trying to flame you, I`m just trying to point out there is a chance of error in any system and to state one is the only way that always works is a mistake. To point out the error one made with any one of them is a good alert to the rest of us as to the possiblity of a bad judgement on our partwhen useing it. It doesn`t mean the method is at all faulty or prone to failure.  | |||
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Scott, I have not been able to check with the aformentioned competitors yet. I will send you a PM as soon as I can. To Everyone Else, Where can I find a decent blade micrometer calibreted to 1/10000 inch. The best I have been able to find around Boise Id uses 1/4 inch round studs instead of blades. It is darned tough to get a decent expansion measurement with them. | |||
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IS, a google search for "blade micrometers" will give you a number of machine tool suppliers that will sell them mail order. Shop around for the best price. The following link is just an example of one that hade them: http://www.msdiscount.com/frame.aspx?session_id=836154194&pdf=369-380.pdf good luck...........DJ | |||
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Quote:Hey Ol` Joe, Yes, that is the portion of "Hired Gun's" post I was refering to. Just went back to find it myself and copy it over here, so you saved me the effort. Quote:Perhaps you have missed my point. I believe I said in reference to the chronograph and the HSGSs that they "can be misleading". If that is not what I said, that is what I intended to say. Quote:I completely agree. A person just beginning to use a "new to him" chronograph, who arbitrairly picks a random Load from a Manual and then just dumps in Powder until he reaches a random Velocity is the exact person I'm talking about. When a person uses multiple Pressure Indicators as you, DJ and others in this thread have mentioned, there is no doubt in my mind they would pick up quickly that something was wrong. But, those are not the people my posts concerning the "potentially misleading" chronographs and pitiful HSGSs are intended for. Quote:I do have Ceramic Gauge Blocks(Mitutoyo Cera Blocks Grade FS), but you do not need them to Calibrate or re-calibrate a 0.0001" capable Micrometer. Quote:You have jumped in past a lot of posts/threads where I mentioned "Averaging" the PRE readings. When done properly, the PRE Method is totally reliable, repeatable and very accurate. If it wasn't, I sure wouldn't be telling everyone how great it is. What may also be confusing to many is a chronograph or a pitiful HSGS gives readings such as 31XXfps and 50,XXXpsi. From this it is implied that the "X" values are significant. That in turn fosters a "misunderstanding" of the actual accuracy level possible, even when everything is set-up correctly and done properly. The pitiful thing is that the people who actually understand "why" this is true rarely mention it. Quote:I didn't take your post as mean spirited at all. And I totally agree that mistakes can happen in any Method used. One of the things I normally include in these threads is that a person should use every Pressure Detection Method available to him. Compare the results of each against the others and if anything indicates a potential problem - STOP and determine what caused the abnormality. DJ mentioned that previously when he listed all the things he watches for, so I saw no reason to be redundant. However, it doesn't hurt a thing to repeat the important part for the Beginners. HSGS = Reloaders Pyrite(aka Fool's Gold) | |||
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It boggles my mind somewhat, that there seems to be a whole lot of us that, if SAMMI standards state a max of 60,000, want to stop our loads at no less than 59,999. I guess that is a little like saying "If the law lets me pound down tequila until I can't walk, then by golly that's what I am gonna do." Then again, it may be the reason the magnums are so popular; that we can drive a bullet a few dozens of FPS faster so that's the caliber I gotta have. If you're comfortable shooting loads that exhibit exessive pressure just to get your chronograph to register what the manual says is max, go ahead. Please don't shoot on the point next to me! For myself, if I shoot 3 consecutive rounds that flatten the primer completely, I consider that load to be too hot or right at max, regardless of what Mr. Oehler says. I'm content to have an accurate load, even if I have to lob the bullet downrange. | |||
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Hot Core, if chamber dimensions, case hardness, case size, etc, are all part of this "handloaders pressure measuring system", how come they are not included in any of your sermons? Specifically: Please identify the relationship betweeen brass hardness and brass expansion, at a range of pressures. Please identify the relationship between case size, chamber size, headspace size of the brass and the rifle, and brass expansion, Please identify the method you use to determine case hardness; Please identify the methods you recommend to measure the chamber dimensions. How do you account for shrinking of the chamber casts at different temperatures? Please identify the relationship between the # of firings and case growth, and the statistical level of reliability of the relationship you have identified. What is the relationship of brass composition within this equation? Again, without measuring, quantifying and identifying the relationship between these variables, and possibly others, the only thing measuring brass will tell you is the size of the brass. Dutch. | |||
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Denton, Thanks for the information. By the way, what is your system sensitivity? By system I am referring to the barrel? The sensitivity is VERY important in determine the actual accuracy potential of the strain gage system, whether you are using potential or resistance type gaging. Thanks again. ASS_CLOWN | |||
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Unfortunatly "reading" the classic "pressure signs" would not work well in your case as damage to the "op rod" would probably occur before these signs became aparent. Of course the "strain gauge" option would probably be best, but if you have a chronograph and access to "Quickload" (or someone that will run some data for you) you can use the predictions coupled with real world chrono data to estimate pressure. Load manual data might not work because the data might not be valid in your case. Of course you could use the chrono data coupled with the pressure/velocity data from manual data the same as you would use "Quickload" data. When I am using "Quickload" data, I start low and work up, stopping below the velocity values that are the "ceiling" that I have established with "Quickload", For examlpe: I load 280 Rem to 7mm Mag pressure ceiling. "Quickload predicts that @ 62,500psi, my load combo in my rifle useing the actual H2O capacity of my cases , should yield a little more than 3,200fps. I stop when Mv aproaches 3,150fps, regardless of powder charge. This has usually worked for me. Occasionally (rarely) pressure signs will become aparent before the velocity ceiling is reached. I have gotten good brass life and no ill affects using this method. It would still require caution, but at least you would have some idea where you were before "pressure signs" showed. | |||
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The important issue is signal to noise ratio, since that establishes your repeatability. The peak reading off the gage is in the neighborhood of 500 microstrains (that's the expansion of the barrel). At that, the voltage out of the bridge is a couple of millivolts. Without running the math, the S/N looks like it's in the 100:1 area. | |||
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Quote: This is an unfounded assertion. It is directly contrary to experimental results, and light years beyond the modest claims Ken Waters made for the system he popularized. Totally reliable? How would you establish that? Repeatable? Yeah, it will reliably repeat within plus or minus 15-20,000 PSI. Accurate? A strange claim for a system Ken Waters, the "father" of the system, said could never reveal actual pressure in CUP or PSI. Egad! A two new ones for the Hot Core list! "Refuses/fails to provide data or references to support his statements.", "Misquotes well-known authors, who do not actually support his conclusions." Thank you so much! How could I have been so slow to recognize this constant behavior? I'll add it to the list right away. | |||
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CDC, I am not an engineer, and I did not stay at a holiday in express last night... However, I do believe one can calibrate a strain gauge without a "known" pressure event. One would have to fire a string of shots, and measure both the strain gauge and the velocity of the individual shots. We know (from, for example, the Powley equation), the relationship between pressure and velocity. Since this is a non-linear relationship, we should be able to bootstrap back to absolute pressure statistically. JMO, Dutch. | |||
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Dutch, the problem with that is the assumption that the Powley equation (or any empirical equation) correctly expresses the pressure. Velocity is a function of average pressure during the travel of the bullet down a bore, and we are looking for peak pressure for safety. And yes, there are many ways to calibrate systems. I used the factory ammo as a tounge in cheek way to show someone that his 'calibration method' is equally suited for strain gauges. It is, however, far preferable to calibrate the system using an actual known input of the same type. Anything else adds to the total uncertainty...and therefore adds to the potential for long useless arguments on forums!  The next best way, IMHO, for the home user is to obtain a calibrated oscilloscope and parallel off the signal. Compare the scope to the trace on the software and correct accordingly. Simple, huh!?!? Other methods, like reading the resistance with a good DMM and such can add to the confidence, but I would have a hard time calling them a true calibration. Of course, I work in an industry where .02% of full scale is considered minimum acceptable accuracy....  | |||
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WOW!! There is a ton of good info in this thread. Now lets make it a little more interesting; 1 Will pressures be noticably different in a chrome-moly barrel versus stainless? 2 Does pressure increase/decrease/stay the same with different lengths of a barrel? 3 Does pressure change at different locations on the barrel? 4 Does overall barrel diameter make a pressure difference? Thanks again, like I said, this thread has been great. | |||
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CDH, I don't see the "problem" as you call it, with accepting a mathematical representation of the pressure gradient. Powley, and those standing on his shoulders, such as Helmut Bromel have developed the mathematical models to a point that makes using them quite rational. They have been emperically tested and found to be eminently useable. 0.02% error? Nope, but within a couple of %. With rational handloading practices, that's a couple of thousand PSI off. If you aren't shooting a Sako, that level of accuracy will keep you safe..... Of course, I am an economist, and anything within 10% is a lot better than a role of the dice (or micrometer, in this case ). JMO, Dutch. | |||
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Quote: I guess I am more comfortable with measured data than calculated data. I had too much trouble with all the 'formulas' in college in classes like thermodynamics giving 'accepted results' and then finding out that they were at best +- 10%, usually +- 50% and sometimes orders of magnitude. A good engineer could come up with something that close by feel and experience, and by the time one uses a 100-300% safety margin, why bother with the calculation! I just trust direct measurement more, as I have a better 'feel' for it! Of course, that and $1 might get you a bowl of soup somewhere... 1-2kPSI is close enough, 5-10kPSI of some systems isn't for any rifle next to my face! | |||
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Scott, Here's a link that will probably have the answers to your questions. It's the web site were they sell the PressureTrace device. http://www.shootingsoftware.com/pressure.htm http://www.shootingsoftware.com/tech.htm | |||
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