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Thread: Powder Burn and Pressure Relationship

  1. #81
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    44man's Avatar
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    This might be one of the greatest discussions ever! But will we ever know? Still, just talking about it as so interesting. I hope it continues but I am starting to lose ideas.
    To just see everyone come together has been great.

  2. #82
    Boolit Master
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    this is gonna be linked to my something that may help sticky so it doesn't get lost in time.
    hopefully the discussion keeps on going.
    it's all an educated guess,,,, till the trigger is pulled.

    this opinion brought to you by mister low-tech solution..

  3. #83
    Boolit Master 303Guy's Avatar
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    I found unburned kernels in the barrel, case and on the catch rag.

    Well, I did that test with covering some powder with sand with some exposed. It ignited just fine and burned slowly with a nice flame then died down and fizzled in the covered bits releasing heaps of smoke. I think what we see when we burn powder in air is just that - powder burning in air, using oxygen from the air. So, confined powder fizzles for a while, producing combustible vapour or smoke which will take of in a big way when the oxygen level gets high enough and the temperature and pressure gets high enough which should be pretty quick but not quite instantaneous. A SEE is beginning to look like no mystery. If that powder fizzles and produces a combustible mixture while the bullet isn't moving fast enough it could suddenly catch and burn too rapidly for the bullet to accelerate and explode. I have seen a powder doing a fizz-bang thing in a Martini Henry. That was just a 'undeveloped' SEE. And every shot did it. I'd say with the right load one could produce a SEE with every shot (and gun - one SEE per gun).

    Anyway, I'm about out of speculations and now need some facts or proof or at least strong indications. Are there any combustion chemist out there to inform us?
    Rest In Peace My Son (01/06/1986 - 14/01/2014)

    ''Assume everything that moves is a human before identifying as otherwise''

  4. #84
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    Doc Highwall's Avatar
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    Check out this page just over half way down and look at the pressure spike.

    http://shootingsoftware.com/

  5. #85
    Boolit Master 303Guy's Avatar
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    Yup. That's the one. They are not all that severe and are sometimes right close to bullet exit. I'm planing on attaching a load cell to my barrel and connecting it to a recorder for play back through my PC. I won't be able to measure pressure but a line on a graph is what I can get with no values.
    Rest In Peace My Son (01/06/1986 - 14/01/2014)

    ''Assume everything that moves is a human before identifying as otherwise''

  6. #86
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    Quote Originally Posted by Doc Highwall View Post
    Check out this page just over half way down and look at the pressure spike.

    http://shootingsoftware.com/
    That knocked me off my seat----120,000 psi? Why from a worn barrel?
    (There are simply too many variables unique to each firearm and a "theoretical" peak pressure has little value for optimizing loads.) This is the truth.
    I never got quick load to load on my computer and it might be good for some stuff. A friend is using it to go crazy with a revolver, he scares me. I just don't know if I would trust the program.

  7. #87
    Boolit Master popper's Avatar
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    303guy - load cell or strain gauge? I saw they had a BT gauge setup, don't know how well that would work. Biggest problem is calibration. I suppose one could use a hot factory load to get max and go from there. Larry G ran some of my loads through his rig, confirmed they were giving a double report, 2nd was at the exit. Every once in a while I use the Powley computer to ball park some loads. Unfortunately they don't have many powder selections.

  8. #88
    Boolit Master 303Guy's Avatar
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    Brain hickup! Strain gauge is what I meant. No chance of my calibrating it and I don't need to. It's the shape of the trace that matters and simultaneously measuring the muzzle velocity would give an indication of the mean pressure which can be used to give a value to the x-axis and y-axis. I'd be more interested in the y-axis, that being the time axis as I could then see where in the barrel peak pressure occurs and the pressure rise rate in the throat area. The idea is to see how different powders and different loads behave. Powder burn consistency would be observable too which I consider very important.

    I once played with two powders in a 303. I plotted powder charge against velocity and found that one powder produced a gentle curve which could be fitted to an equation while the other powder produced a curve that went ballistic as I increased the charge with velocity increases out of proportion the the powder increments. From that I saw the danger of an overload with that particular powder and also the sensitivity of small powder variations at higher end loads. The first power on the other hand was wonderful stuff with consistent velocity increases with powder increments, indicating relatively low sensitivity to to small powder variations. Indeed, that powder produced shot to shot variations of 3 to 6 fps in two guns, my mini-14 and my 303 Brit. In fact, the velocity spread could be attributed to the accuracy of my chronograph which had a resolution of 1 m/s (3 fps). It was an accurate powder at the target too. I could hit a beer can (empty) at 200 meters!

    Why would a worn bore produce such a massive pressure spike? One can only speculate but I wonder whether it has something to do with lack of bore resistance allowing the expansion rate to be too great to build up enough pressure earlier in the bore. I see that result as being of high significance. I would have been great if those guys had increased the powder charge to see how that spike would have responded. It might have disappeared or gotten much worse.
    Rest In Peace My Son (01/06/1986 - 14/01/2014)

    ''Assume everything that moves is a human before identifying as otherwise''

  9. #89
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    Strain gauges are already "calibrated" when you buy them. I don't know about the software used in pressure spike site but with the Oehler M43 the "calibration" data is input into the program. Additionally Dr. Oehler recommends the use of factory ammuntion as a "reference". Unfortunely many confuse the use of "reference ammunition" with calibration. I was fortunate when contacting Federal and Winchester to get the psi data (transducer) and conditions for several lots of factory ammunition from each that I had. With that it was very easy to see when testing that factory ammuntion the M43 was quite accurate. Factory "reference ammuntion" (a lot of factory produced ammuntion that demonstrates quite uniform internal ballistics that is then set aside for use as "reference ammunition") is very expensive and hard to obtain.

    I also test as many different factory and milsurp (if available) cartridges for each cartridge I test. This gives a baseline to compare the handloads with both velocity and pressure wise. Additional I have a large lot of M118SB that I use as "reference ammunition". Each time I set up the M43 a test string of 7 shots is fired with that rifle and the same test rifle. If the results are not within the varience of different test strings and condition variations then I know something isn't correct and it is corrected before the test is run.

    BTW many mistakenly believe that every factory cartridge is loaded to the SAAMI psi MAP level; such is definately not the case. Very few factory cartridges, even after calculating the "reference" offset, are at the SAAMI MAP. The psi of most factory cartridges in commercial chambers is considerably below the SAAMI MAP for the cartridge. Factorys leave a fudge factor (for good reason) in the psi level.

    Larry Gibson
    Last edited by Larry Gibson; 04-12-2013 at 02:46 PM.

  10. #90
    Boolit Master
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    Larry, the strain gages that come with the RSI unit have a gage calibration factor to input into the program.

  11. #91
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    Can I get crazy? How about a row of strain gauges from the chamber to the muzzle to read the whole pressure trace.
    One LU or CU or strain gauge reads pressure at one spot and peak can be before or after it's position.
    The slope away from peak can not be read over distance. You only see what the strain gauge sees at it's position.
    You will see strange stuff with a strain gauge when pressure returns to give a spike. This will not be seen with CUP. CUP is static as is LUP. The lead or copper crush positions are not changed with powder types that change peak distances. They ONLY read chamber pressure at where the crusher is positioned.
    How much different is a strain gauge position? Is it at peak, before or after?
    Since each powder is different, should not the strain gauge be in a different position.
    We need a long gauge from chamber to muzzle.
    Last edited by 44man; 04-12-2013 at 04:19 PM. Reason: spelling

  12. #92
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    Like the dictionary definition of SEE, the dictionary definition of expansion ratio means nothing to us as well. Reason: the definition does not include the function of TIME! We, on this board, are interested in dynamic definitions, not static definitions. In other words, the rate of change of something is paramount to our definitions, questions and answers. In other words, being late to this thread, I need to know what the various premises are before I can respond with my proverbial short answers. ... felix
    felix

  13. #93
    Boolit Master
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    44man, the strain gage is attached over the middle of the chamber. The outside of the barrel dimension along with the outside of the cartridge/inside of the chamber dimension is input to within .001" so the actual wall thickness where the strain gage is attached, and finally the case wall thickness is input for that barrel.

    Because the strain gage is attached over the center of the cartridge and the known thickness of both the steel barrel and brass cartridge are known the strain gage can read real pressure in real time. As soon as the primer fires the strain gage starts to record pressure and will continue until the bullet exits the muzzle.

    Click on the web site I posted above and look at the traces, you will see that with chronograph input of muzzle velocities that it will show where the bullet exits the muzzle.

  14. #94
    Boolit Master 303Guy's Avatar
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    But is is possible for the pressure to be different at different positions in the bore? That's not too crazy if one has a look at gas laws as pertaining to gas flow through a nozzle. is that pressure spike being caused by a gas pressure wave rather than detonation of a combustible mix of gasses made up mostly of burned gases? One must ask where the energy is coming from to generate that pressure spike.

    My idea with the strain gauge is to simply plot current against time and obtain a curve. If I can compare that to a factory cartridge to give some vague pressure meaning to the curve then fine but for me it's going to be about the shape of the curve, not the actual pressure producing it. Knowing the velocity will give some meaning to the area under the curve but that's about it.
    Rest In Peace My Son (01/06/1986 - 14/01/2014)

    ''Assume everything that moves is a human before identifying as otherwise''

  15. #95
    Boolit Master
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    303guy, look at my post #84 and go to the web site and save it under your favorites. If you read all the way through it you will see it gives other sites as reference to what can be done with this equipment.

    I was sold on it and when I had my money saved I purchased it and now I am a happy camper. It will open new doors as to your understanding of internal ballistics.

    What I thought I knew, I now know differently with a much better understanding.

  16. #96
    Boolit Master 303Guy's Avatar
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    Thanks, Doc Highwall. I do have that one saved to my favourites. It will be sometime before I can lay out the cash for one of those but I do agree that it is the way to go. But until then I want to connect a strain gauge to my PC via a USB oscilloscope adaptor. One can view a trace using an audio oscilloscope software package such as Nero.

    What I need too is a means of chronographing inside my test tube. I do have some ideas that will utilize my Chrony.
    Rest In Peace My Son (01/06/1986 - 14/01/2014)

    ''Assume everything that moves is a human before identifying as otherwise''

  17. #97
    Boolit Master popper's Avatar
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    The strain gauge doesn't measure pressure, as we are using it. It measures expansion of the chamber. Chamber measurements and some hidden calculations give pressure. Pressure between the bolt and the CB 'should' be the same so there is no reason for a long or several sensors. But velocity might be measured by multiple sensors.

  18. #98
    Boolit Master 303Guy's Avatar
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    I have heard of multiple sensors being attached. The secondary sensors would confirm the primary trace values and would indeed measure the velocity - with a little bit of math.
    Rest In Peace My Son (01/06/1986 - 14/01/2014)

    ''Assume everything that moves is a human before identifying as otherwise''

  19. #99
    Boolit Master
    Doc Highwall's Avatar
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    popper, the RSI unit I have converts the strain into direct pressure in P.S.I. and gives both Time and Pressure for the whole trace till the bullet exits the muzzle.
    Click image for larger version. 

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  20. #100
    Boolit Master popper's Avatar
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    converts the strain into direct pressure in P.S.I.
    No disagreement intended it just takes some calculations. I was merely stating how they work. Different from a direct 'pressure' load cell measurement. I've derived fps from pressure measurements, I was thinking more about time of transit between 'bumps' of pressure when the bullet passes.

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BR Bench Rest M Magnum RN Round Nose
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