Burn Rate mystery

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by RustyRick, Jan 21, 2014.

  1. RustyRick

    RustyRick Well-Known Member

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    As I look at my supply of powder, my loading manuals, my caliber and a burn rate chart I find one missing bit of information.

    For example. How much slower is IMR 4831 than Hodgen 4831. Or how much faster is H4350 than H380.

    I phone Hodgen to day and I understand the difficulties in objectively rating a powder.

    However I think (over simplified I'm sure) that SAAMI should do a spread sheet and index the middle or average burn rate at 100. And then rate each powder as a percentage either over or under.

    Then one would be able to experiment with other powders with some degree of foundation and fudge factor.

    But it would also answer why in any given manual you see limited number of powders recommended when you know others would work too.

    Just wondering ....:cool:
     
  2. Lefty7mmstw

    Lefty7mmstw Well-Known Member

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    imr 4831 is faster than h4831 by a good bit.

    That said, you are never going to get any definitive "spreadsheet" as powder burn rates have a habit of changing as bore diameters change, load (bullet weight) changes, pressure changes, etc.. The best you are likely ever going to get is a burn rate chart like you've already seen.
     
  3. safarihunter

    safarihunter Well-Known Member

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    I think that you will also find that there is a variation in "batches" as powder is manufactured.
     
  4. Lefty7mmstw

    Lefty7mmstw Well-Known Member

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    +1...
    that too. That's the reason they tell you to back off a bit and re-work every time you buy new lot # components.
     
  5. mitch260

    mitch260 Well-Known Member

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    On quickloads they list a burn rate factor. A higher number indicates a faster burn rate. For example RL-17 has a burn rate factor of 0.4700, while RL-19 has a burn rate factor of 0.4500. IMR4831 has a burn rate factor of 0.4421 and H4831 has a burn rate factor of 0.4301. I would say that a spreadsheet could be made.

    Actually I just went back and looked at it again, and the numbers stated above only apply to the very first stages of the charge being burned. there are other factors that have different meanings in relation to the powder being burnt, but it gives you an idea anyway.
     
  6. RustyRick

    RustyRick Well-Known Member

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    Now your talking my language.

    There has to be mathematical data to even come up with a burn rate chart in the first place. Or else someone would be HUGLY liable just producing the chart.

    Therefore it stands to reasoning that a ballistician/mathematician should be able to relativize the list to some degree. Not withstanding the variables which would produce a +/- range anyhow.
     
  7. Kennibear

    Kennibear Well-Known Member

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    Be VERY careful about assumptions! Pressure has a HUGE effect on powder burn rate! Some speed up at 40Kpsi - 50Kpsi and others hold steady until 65Kpsi. Pistol/shotgun powders can go nuts as low as 30Kpsi. That's why there is only a general relationship to burning rate. Powders like Superformance and Leverevolution are even more specific. H4831 was designed around the original burn rate of the surplus stocks that Hodgdon's sold in the '50s. IMR 4831 was the update DuPont came out with decades later just like H4895/IMR4895 except those two are closer in burn rate.

    I use the burn rate charts all the time but I start low and inch up real slow like!

    KB
     
  8. J E Custom

    J E Custom Well-Known Member

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    All good advice.

    On My Website- jecustom.com - I have a link to a good burn rate chart that helps but it does not tell exactly how fast the powder burns just its relationship to other powders.

    It also shows other powders that fall between IMR and Hodgdon if you are looking at another powder. this helps to locate new powders in the same range that were not available a few years
    ago.

    If you are shooting MAX loads you should always start a little lower even if you are using the same brand because of batch differences.

    Powder manufactures don't want to give to much information because of liabilities.

    J E CUSTOM
     
  9. RustyRick

    RustyRick Well-Known Member

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    Interesting, I'd ALSO expect Burn Rate Charts to be split up between recommended usages. Pistol, Shotgun, Rifle, an maybe Black Powder. I don't know if they are included in my H Chart.

    I think I recognize pistol and shotgun powders in the same chart as rifle. I've never been able to compute that.
     
  10. Lefty7mmstw

    Lefty7mmstw Well-Known Member

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    some powders have application in more than one firearm type. h110 and 4227 are two great examples of this. I've shot 4227 in my 44mag and in my '06 with cast bullets. Most people use h110 for 44mag, but the original use was 30 carbine(rifle) and it can be used in the hornet and in 410 shot shells.
     
  11. RustyRick

    RustyRick Well-Known Member

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    It's still simple. Put those dual use powders an multiple charts.

    However you said "That said, you are never going to get any definitive "spreadsheet" as powder burn rates have a habit of changing as bore diameters change, load (bullet weight) changes, pressure changes," etc..

    I'm sure, at least I would hope, powder manufactures rate "burn rate" on an objective, and replicatable scientific process. That would likely mean that they use a base volume or weight to test ALL powders.

    They would have to take as many variables out of the equation as possible.

    What you are referring to is in the field response to a huge variety of variables. Of course pressures are relative to bullet weight, bore diameter, and even ambient temperature.

    But I would have to believe BURN RATES are "Test Lab" research based on locked down protocols.

    I rest my case.
     
  12. Kennibear

    Kennibear Well-Known Member

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    The protocol is called a " closed bomb test" with a high tensile strength steel sphere w/ pressure gauge. Fixed amount of powder is set off and pressure curve is recorded. Secondary after that is a SAAMI test gun firing.

    Another factor is energy density. Separate from the load density double based powders have more energy per unit weight. Even though the burn rate is the same you use less as DB powders have higher energy content.

    It's just very complicated to reduce it all to a single table. Hodgdon puts out a good rate table and their 2014 Mannual/Magazine just hit the stands. Got mine yesterday.

    KB