Lighter bullets require smaller powder charge to avoid over pressure

Discussion in 'Ammunition & Reloading' started by dgang, Nov 7, 2019.

  1. dgang

    dgang Member

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    While loading some 7.62x39mm with 125gr. FMJ using 30gr. of H335 I noticed Lee's load guide advising not to use that amount of powder with a lighter bullet in order to avoid overpressure. It seems contrary to my experience. I thought a heavier bullet of the same construction requires less powder to keep the pressure at safe levels.
    Does anybody have an explanation for this contradiction?
    Thanks in advance, dgang.
     
  2. Rifling82

    Rifling82 Well-Known Member Supporter

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    I've always thought of it like this...... A lighter bullet needs more thrust (powder) .... Like throwing a light weight rock, to get it to go farther you have to throw harder..... I have no clue if I'm right or not
     
    Last edited: Dec 27, 2019

  3. dgang

    dgang Member

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    According to Lee's load guide a 108gr. jacketed bullet load is max @ 28.8 gr. of H335. A 125gr. jacketed bullet is max @ 31.5 of H335. Both loads are right at 40,000 psi.
     
  4. PaBushMan

    PaBushMan Well-Known Member

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    With rifle loads a heaver bullet can call for more powder in some instances. I use more than one manuel. I always cross check loads.
     
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  5. OldManMontgomery

    OldManMontgomery Active Member

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    A lighter bullet generates less pressure, ALL OTHER FACTOR REMAINING EQUAL (being the same). The difficulty is a lighter bullet may be more efficient with a different powder. A lighter bullet with a solid core will usually generate higher pressures, so be careful with that aspect.

    Read the fine print. They might be thinking of something I haven't noticed.
     
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  6. dgang

    dgang Member

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    OldManMontgo:
     
  7. OldManMontgomery

    OldManMontgomery Active Member

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    Dgang, powders are used in accord with their burning rate, 'speed'. N335 is one of the powders I see listed for 7.62x39mm in the Lyman #50 book.
    I looked in the Lee manual I have (#2) and 7.62x39mm isn't listed. So the comment you mention is not listed, either. I do have Lee dies for the round. Powder charge is not given for H335 in the listing included.

    BUT, in the Lyman #50 manual it shows 30.5 of H335 as a starting load for a 123 grain bullet (in my experience that difference means little or nothing). I also note the starting charge of H335 with a 130 grain bullet is a grain lighter (29.5 grains). Not a problem.

    The Lyman manual also suggests H335 gives the best accuracy in their trials.

    In short, H335 is fine to use as you intend.

    I confess I am still puzzled about the lesser weight bullet gives higher pressure comment. I cannot make sense of it.
     
  8. jpattersonnh

    jpattersonnh Well-Known Member

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  9. locutus

    locutus Well-Known Member Supporter

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    Generally , but not always, lighter bullets use HEAVIER powder charges.

    But there are many factors other than bullet weight that influence pressure and velocity.
     
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