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Why do we use more powder with lighter bullets?

Discussion in 'Handloading and Reloading' started by 0to60, Jun 23, 2013.

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  1. 0to60

    0to60 Member

    Feb 22, 2011
    ...and less powder with heavier bullets?

    I can think of two possible reasons for this:

    1) A lighter bullet takes less pressure to start moving, and once it does the "combustion area" becomes larger, thus reducing pressure. By adding powder, we can keep burning into this expanding space, increasing the amount of energy imparted to the bullet.

    2) A heavier bullet is longer, and thus seats deeper into the case, raising pressure. To compensate, less powder is used.

    Am I close?
  2. rcmodel

    rcmodel Member in memoriam

    Sep 17, 2007
    Eastern KS
    Sort of close.

    Inertia, and bore friction are both very important reasons.

    Try hitting a Soccer ball and a Bowling ball with a doubled up fist as hard as you can, and it will quickly become clear to you!

    You can hit the lighter soccer ball harder without breaking your fist.
    And it will go faster then the Bowling ball if you hit it harder.

  3. Sam1911

    Sam1911 Moderator

    Oct 22, 2007
    Central PA
    Pressures. As rcmodel says, that heavy bullet has a lot of inertia, and more friction to overcome before it gets moving.

    Fire off a max charge appropriate for a light bullet under a heavy bullet and the pressure will go way above what the barrel should have to handle before that bullet is started moving, and will continue too high until the bullet is out of the bore.
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