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Powder Drop/Weight Change

Discussion in 'Uncategorized Threads' started by phirel, Feb 1, 2008.

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  1. phirel

    phirel TS Member

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    Last week we had an interesting thread about the affect of humidity on the weight of the powder that was dropped by reloading machines. To investigate this question I did the following experiment. I weighed out 20 charges of American select powder dropped by my press. The 20 charges varied in weight from 17.6 grains to 17.9 grains. I placed each charge into a plastic container that was about 1/2 cubic inch and had an open top. The powder was distributed uniformly across the bottom of the cubicles.

    First, I let the charges sit in an unheated room and exposed to the cold winter dry air for two days. After this time I weighed the charges again. Seventeen of the 20 charges had the same weight. Tow charges decreased in measured weight by 0.1 grain and one charge decreased by 0.2 grains. None of the samples gained weight. Any weight change less than 0.1 grain was ignored. I have no idea if the decrease in weight was due to weight loss or expire mental error.

    Then I placed the 20 charges in a plastic storage tub with a snap on lid. I left 10 of the samples open to the air in the tub. I placed the other 10 samples on a sheet of glass in the tub and covered them with another plastic shoe storage box. I put a hand towel saturated with water in the tub and snapped on the lid. It was my intent to expose 10 samples to 100 % humidity and 10 samples to 100% humidity but protected in a closed container much like we store powder in our reloading machine powder hopper. The tub was stored for two days in a heated section of my house (ca 70 degrees F). I then weighed each of the 20 samples.

    All samples exposed directly to 100% humidity air gained weight. The weight gain varied between 0.3 and 0.6 grains. The total weight of the 10 samples exposed directly to the 100% humid air was 177.4 grains before exposure and 181.6 grains after exposure.

    The 10 samples stored in the high humidity tub but protected from direct exposure to the humid air also did show some weight gain. The gain varied from 0 to 0.3 grains. The total weight of the 10 samples before exposure to the humid air was 176.7 grains. After 2 days, the total weight of these 10 samples was 179.6 grains.

    My conclusions from this rather crude experiment were that American Select powder can gain weight if exposed to humid air. It gains less weight if it is exposed to humid air while stored in a partially sealed chamber similar to a powder hopper found on a typical reloading machine or in a partially filled factory powder container.

    These findings could provide some insight into why a powder bushing will drop different weights of powder on different days.

    Pat Ireland
     
  2. j2jake

    j2jake Well-Known Member

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    Pat, what about temperature change of the bushing? I have noticed that drastic variances in ambient temps has had effect of the same type. Just an observation with no scientific study. Jake
     
  3. stokinpls

    stokinpls Well-Known Member

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    Does that explain the higher scores shot in the desert?
     
  4. phirel

    phirel TS Member

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    j2jake- Temperature changes would affect the size of the hole in the bushing, but I doubt the change would be great enough to alter the powder volume dropped. My powder bushings fit snugly into a plastic housing and I have not noticed any difference in the way they fit into this housing at different temperatures.

    Pat Ireland
     
  5. johara1

    johara1 TS Member

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    Pat,as a old bench rest shooter and big bore shooter,you will find that powder droped by volume is more accurate than powder measured by weight..2 grain is the norm by weight for a rifle....jim
     
  6. johara1

    johara1 TS Member

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    Pat,as a old bench rest shooter and big bore shooter,you will find that powder droped by volume is more accurate than powder measured by weight..2 grain is the norm by weight for a rifle....jim
     
  7. zzt

    zzt Well-Known Member

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    Thanks for the work Pat. Numbers are always better than supposition. If I can find enough suitable containers, I'll repeat your experiment with Green Dot. For some reason, that powder seemed to show a more pronounced effect.
     
  8. johara1

    johara1 TS Member

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    Pat,as a old bench rest shooter and big bore shooter,you will find that powder droped by volume is more accurate than powder measured by weight..2 grain is the norm by weight for a rifle....jim
     
  9. phirel

    phirel TS Member

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    zzt- I am very interested in the results of different powders. Last week we got into a discussion of surface condensation equilibrium. Different powders might answer this question. I now wish I had included some round balls of aluminum foil to look at that possibility. I also made the assumption that powder is not hygroscopic, but that might also come into question.

    Pat Ireland
     
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