burn rates

Discussion in 'Reloading' started by rotorhead, May 6, 2007.

  1. rotorhead

    rotorhead Well-Known Member

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    I have looked at several burn charts but they all seam to be different. Does anybody have a sort of scientific burn chart. I'm looking for something that has time burnt type of information. I would like to know the differance specifically between powders. such as H-1000 ans RE-25
    thanks,

    RH
     
  2. britz

    britz Well-Known Member

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    I just happened upon your question and it got me a little concerned. I don't have a scientific burn rate chart, and I will assume that the powders that are not listed in the same order are very close to the same burn rate. Why do you need to know the exact difference? You shouldn't ever use one powder to substitute for another anyway.
     

  3. CatShooter

    CatShooter Well-Known Member

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    [ QUOTE ]
    I have looked at several burn charts but they all seam to be different. Does anybody have a sort of scientific burn chart. I'm looking for something that has time burnt type of information. I would like to know the difference specifically between powders. such as H-1000 ans RE-25
    thanks,

    RH

    [/ QUOTE ]

    Burn rate charts are very close approximations.

    The reason that some powders will swap positions from one chart to another is that the determination of burn rates is not an exact science. Also, because stick and ball powders have different basic designs, they have different advancement rates, which means that at 45Kpsi, "A" will burn faster than "B", but at 55Kpsi, "B" will burn faster than "A".

    The good part of all of this confusion is that if two powders exchange places, it's because they are so close in burning rates, as to be just about identical.

    .
     
  4. goodgrouper

    goodgrouper Well-Known Member

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    There are many reasons why all the burn rate charts are a little different. First of all, they primarily test "quickness" of a powder in controlled pressure/time test bombs to establish the rate instead of cartridges. These tests tell them all the scientific mumbo jumbo that the engineers need to know and what they must figure is more than what the general public needs to know.

    Then after testing the powder for quickness, they will test it in a variation of cartridges to see what other characteristics it demonstrates.

    Another reason for the burn rate chart confusions is the differences in lot to lot consistency. Your particular lot may be faster or slower than their lot. And they may have tested it in a different caliber entirely which also can change the rate. Powders burn rather slowly in an unconfined space. But confine them and they still burn but it is so quick that it is more like an explosion. So it would make sense that the burn rate would change a bit depending on how much space was in your case at time of combustion. In other words, take a powder like say H4831 and stuff it into a 223 and compare pressures to a near casefull in a 300 win mag. The burn rate changes slightly.

    Many of the quicker rifle powders are tested in 243 winchesters so if you are shooting a 6br or a 6mm-284, your results with the same powder will be slightly different.

    And another reason for the chart variations is time of print. An older chart (even from just 5 years ago) is so outdated with all the new powders out now that it will have powders in different places.


    FYI, the last time I talked to Alliant, they faxed me a spec sheet from one of their pressure bombs that compared RL22 to RL19. Most of the info on it may has well been in hyroglyphics but I was able to see a 3% difference in those two powders and lots.
     
  5. rotorhead

    rotorhead Well-Known Member

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    [ QUOTE ]
    I just happened upon your question and it got me a little concerned. I don't have a scientific burn rate chart, and I will assume that the powders that are not listed in the same order are very close to the same burn rate. Why do you need to know the exact difference? You shouldn't ever use one powder to substitute for another anyway.

    [/ QUOTE ]
    Britz,I'm just interested in why they are all different I don't substitute one for the other and I don't just assume anything from one pound to another.

    Thanks Goodgrouper and catshooter you've explained it well. This was as much of a couriosity as much as anything.

    Rh
    RH