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Thread: Pressure Question

  1. #1
    Boolit Master

    Johnch's Avatar
    Join Date
    Jun 2005
    NW Ohio

    Pressure Question

    OK I know this just Wrong in so many ways

    But it works ....and lowers my bar bill when others bet me I am full of it

    Well I know 9 mm and 380 ACP are not the same
    Also they have different load data and head size

    But in a screw up (by me) loading 9 mm with a Dillon 550 press
    I loaded some 380 ACP cases with 3.8 gr of HP 38 and a 125 gr cast bullet ....slightly less than the starting load for a 124 gr jacketed bullet
    But at the same OAL as the 9 mm load I was loading

    So to not waste anything I shot the loads in my Glock 22 ...Err 17 .... I switched barrels
    I also shot some in the High Power

    Worked just fine

    Not as good of a group
    Just had a different POI

    Not in any way plan on shooting a any more of this loading as the 380 ACP case has a slight bulge IMO due to the chamber size

    BUT I was just wondering what kind of change there would be in the chamber pressure
    As both of the cases were loaded to the same overall length
    But as the 380 ACP case has less case volume

    I would think the pressure would be slightly higher

    Yea, thou I walk through the valley of the shadow of death, I will fear no evil; for thou art with me; Thy rod and thy staff, they comfort me.
    And I carry a SIG

  2. #2
    Boolit Master Bazoo's Avatar
    Join Date
    Dec 2013
    Cecilia, Kentucky
    It wouldn't be much of a difference because the cases are so similar in size internally, and you were at a low level. I probably would have shot them too.

    You could trim a 9mm case the same as a 380 case and measure their respective water capacities.

  3. #3
    Boolit Bub
    Join Date
    Oct 2019
    CA, USA
    As the same OAL i bet the pressure difference is negligent... I would've should them too haha
    Don't let America end up like California...
    "You've got to ask yourself a question: 'do I feel lucky?' Well, do ya, punk?"

    God bless America
    God bless those who fought for liberty

  4. #4
    Boolit Buddy
    Join Date
    May 2016
    I would bet you that pressures would actually be slightly lower.
    The inside of a 9mm case tapers and rounds at the bottom, 380 cases are much more straighter giving them slightly more 'below the boolit' case capacity. (At least i think so without doing any measurements.)
    At any rate the difference is likely negligible.
    Praise the Lord and pass the ammunition.

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Abbreviations used in Reloading

BP Bronze Point IMR Improved Military Rifle PTD Pointed
BR Bench Rest M Magnum RN Round Nose
BT Boat Tail PL Power-Lokt SP Soft Point
C Compressed Charge PR Primer SPCL Soft Point "Core-Lokt"
HP Hollow Point PSPCL Pointed Soft Point "Core Lokt" C.O.L. Cartridge Overall Length
PSP Pointed Soft Point Spz Spitzer Point SBT Spitzer Boat Tail
LRN Lead Round Nose LWC Lead Wad Cutter LSWC Lead Semi Wad Cutter
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