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After reading a lot of these posts as well as some other references I think that I probably should modify my original hypothesis. First of all as one of the top experts in the feild - Ken Oehler says, "I feel sorry for those who think ballistics is an exact science. They just don't understand the problems." Ballistics is an inexact science and gives ballisticians grey hairs (Speer Manual). So trying to predict exact pressures by velocity is probably going too far, though I would still like to test some loads that track with published data in my rifles to see how close or far they are away from the same pressures. I still think that if all the components are the same and the velocities match the pressures should be close but I can't at the moment prove it. I do still think that a chonograph is probably the most useful tool for telling an average reloader when pressures are too high. Case head expansion is another useful tool as is quickload but all too many loads developed using case head expansion when actually pressure tested have been found to be well over limits. I've seen some totally incongruous loads spit out by quick load. The best safest thing would be to use all three. If your velocity is fine and quick load says your powder charge is below max and you have too much CHE, the load is probably too hot. If your CHE is OK and your velocity is too high the load is probably too warm. If all your velocities as you are working up a load match quick load data and it says one load is over pressure it's probably too warm. Call them weasel words or whatever but when it comes to ballistics none of the other experts give absolutes so probably, maybe, might etc. are required terms when describing ballistics. This has been a good thread for the most part without too much trolling. I appreciate your comments, even the ones where we disagree. Thanks for chiming in.............................DJ ....Remember that this is all supposed to be for fun!.................. | |||
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To indicate pressure/temperature when firing a load, I always use a technique similar to when you are aligning gear wheels to make sure they are having correct contact patern, for that you use a marking ink But for pressure/temperature indicator I use a ink pen to mark the brass on it’s base like shown on the picture. The base may never make contact to the chamber (with the stem from your slide gauge you can measure where the base is in your brass)   Thanks Bjarne | |||
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Can you please expand on this. Are you saying that the further down towards the head of the case that the base contacts the chamber, the higher the pressure load? | |||
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Fantastic post!   | |||
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There's a man of my own heart! KenO As it was explained to me many years ago, "I feel sorry for those who think ballistics is an exact science. They just don't understand the problems." | |||
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To infer that velocity tells you everything is just as inaccurate. All of those scientists knew that the area under the curve produces velocity not just peak pressure. | |||
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Ken, Just read your contribution to the Lyman 47th edition reloading manual on chronographs. A lot of the article focused on accuracy of the device and the sun screens but you did touch on this subject briefly, I believe. Have you any more published information relating to this? | |||
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Generalisations Alf ...??  | |||
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You will clearly notice that the brass will contact the chamber closer to it’s base as you raise the pressure Thanks Bjarne | |||
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BlaserGun, Very interesting post, I've not seen this idea before and will probably have to experiment with it. Thanks for contributing...........................DJ ....Remember that this is all supposed to be for fun!.................. | |||
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I thought so, but since you posted pics of two different caliber cases, I wanted to ask. Also there is now way to tell, unless you already know at what pressure each caliber operates, which one has the higher pressure Thank you for the clarification After thinking of it, wouldn't this be like measuring case head expansion? I would think that you wouldn't want that to happen down near the web. | |||
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What BlaserGun has shown a picture of is measurable and is called - Ta Daa - good old never fail PRE. Totally agree. Nice to be able to discuss things, disagree if need be, and get along.  | |||
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The case walls are tapered. If you are using a consistent lot of brass the case wall thickness will be uniform from case to case. But the case wall is tapered and is thicker toward the base. The thicker brass is harder to expand. The higher the pressure goes the further toward the base the expansion ring goes. I have to qualify this a little. If you are shooting a benchrest rifle or something similar where you may shoot a case 15 or 20 times without sizing the body, the repetitive shooting even at the same pressure may also cause the pressure ring to move down toward the head. | |||
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Thanks. Great info. I'm absorbing. | |||
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The 30-06 is with the highest pressure both according to the primer and case expansion to the base, the base is thicker on the 30-06 compared to the 6,5 which is the reason why they differ that much on case expansion. Yes it’s like measuring case expansion at the base, but with this method you will see when the pressure grow, which you only will in the dangerous end of the scale when measuring mechanically, but you can use the same method at the same time and as well chrono your loads. I use this chamber touch method and hold it together with primer expansion and the speed from chrono and the one calculated in Qload To make it clear where you want the expansion to stop you can cut one of your brass in cross section to show where the case starts to get thicker, and I would say it’s somewhere between where it starts to get thicker and the inside bottom of the case that I want the expansion to stop, the closer you get to the base the shorter your case will live  Thanks Bjarne | |||
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Gotta disagree with that simply because it is not true. And completely agree with that simply because it is true. | |||
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Yes maybe that’s too roughly speaking about the difference in these two methods, but what I mean is that you don’t have any expansion on the base of the case in the lower end of the pressure scale, but with this ink method you will see how the contact point move down the case as you raise the pressure from the lower end, with the mechanical you will only be able to measure differences in the upper end of the pressure scale. Only thing I can say about it is, try them both at the same time when building up a load Thanks Bjarne | |||
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Hey BlaserGun,We are back in complete, 100%, agreement. | |||
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Using the inked-case method is interesting and I understand how the chamber contact point will move down the case with increasing PSI, but it still doesn't tell me what is excessive PSI . For me, a practical PSI measuring tool is "measuring" the rapidity of primer pocket loosening. To reload, a case must hold a primer, and I don't want hot gases escaping into my face from a blown primer. Moreover, I don't want to get a stuck case from excessive PSI when I need to get a rapid second shot at my trophy of a lifetime – heaven forbid should that happen. In my experience, rapidly expanding primer pockets occur just before a blown primer; and, blown primers are a prelude to a stuck case. The cost of a case is miniscule compared to the overall cost of a trophy hunt, thus I'm not partial to getting 10-20 reloads from a hunting load. I figure, if I can get 3-5 reloadings per case before the primer pockets get noticeably loose while hand priming, then I'm working within acceptable PSI limits. I only shoot the HOT loads a few times a year - 3 to 6 shots to sight-in and hopefully only 1 to get my game. That is less than 10 shots per year. I’ve never had a problem in field and I’ve been big-hunting for 40 years. For target practice, I load way down into the 40,000 PSI or lower range - targets don't need much killing. Regards, AIU | |||
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I think now that velocity is of overblown importance, even in a hunting situation. I think you would find that hunting bullets will perform well at "not so hot" velocities. Realize that you are slowly damaging your rifle and creating a headspace problem by shooting a hot load. It could end in an accident with no warning signs, as I've read and other posters here have stated. | |||
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All due respect but I think that this method is a pretty sure way to have some of your loads a good bit over normal pressures. I'd really rather have a load that's safe to shoot as much as I want without any Angst about it being too hot and having to limit the # of rounds of it I shoot. If I really need that much more velocity I'll use a bigger caliber. No Animal on earth is going to be able to tell the difference between a bullet shot with 62K psi vs 80K psi but your rifle sure might! .............................DJ ....Remember that this is all supposed to be for fun!.................. | |||
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This is very true, and what I have come across often. The theory that every increase in powder increases pressure, and therefore velocity, is a misnomer. As maximum pressure, or in other words the peak pressure time curve, is surpassed, the max/peak pressure will happen at a significantly different point in the pressure curve, which can stop velocity increasing, and even make it go backwards. I have tested thousands of rounds with pressure equipment in numerous rifles, and pressure does have a relative relationship to velocity, but not as precisely as what is mentioned here. I have had a 300WinMag achieve 3200fps with Nosler 180gr AB's with pressures that were less than 60,000psi in a 26" barrel. The same rifle achieved just under 3100fps with Nosler 200gr AB's, and a pressure of 61,000psi. Does this mean that this barrel is a 'FAST' barrel?, I don't think so, it just shows that it's 4 groove design allowed faster velocities with less pressure, also, the particular bullet used might be 'FAST' for it's weight and amount of bearing surface. The idea that listed velocities at 'X' pressure is going to be the same in every barrel is somewhat correct, but it cannot be said that it's absolute, just the same that 'X' amount of powder with 'Y' bullet will give the same amount of pressure in a hunting rifle as it does in a test barrel. Just my experience. 416RigbyHunter. | |||
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Thank you for some clarification! | |||
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This system can indicate the pressure from load to load http://www.shootingsoftware.com/pressure.htm but I’m not sure how accurate it will be as a pressure scale it self without comparing to other loads in the same rifle. I’ve been thinking about this system to develop shotgun loads. I’ve never really got started because most of my hunting is stalking with the rifle. Thanks Bjarne | |||
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The Accurate Reloading Forums THE ACCURATE RELOADING.COM FORUMS Guns, Politics, Gunsmithing & Reloading Reloading Using a Chronograph as a Pressure Guide...................
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