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Suggestion for 9mm RMR 124 gr JHP load for Auto Comp powder 4.8 grs, OAL 1.10

Home › Forums › General Reloading Discussion › Suggestion for 9mm RMR 124 gr JHP load for Auto Comp powder 4.8 grs, OAL 1.10

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  • January 3, 2025 at 7:03 pm #526372
    caf308w
    Participant

    I received my RMR 124 gr .355 Dia JHPs and loaded a test batch with 4.8 grs of Auto Comp with a OAL: 1.10. They shot well 1 1/2” group at 10 yards two handed forward stance but I am interested in knowing what the powder weight range should be for this buiiet using Auto Comp. Also I don’t have a conagraft to determine the velocity anyone have experience with this bullet / powder combination? Thanks in advance for any help.

    January 4, 2025 at 6:14 pm #526470
    kluthe
    Participant

    I dont use Autocomp but just for grins I looked at various load sources I do have (via powder, bullet manuf etc) and I can’t find any load seated at that OAL. Curious how or why you started at that load…I suppose you have a fair amount of experience with the powder ?

    January 11, 2025 at 7:44 pm #526728
    Gary Smith
    Participant

    @kluthe: If you go to the Hodgdon Reloading Data website, you’ll find AutoComp loads for 124 gr Berry’s and XTPs. The former OAL is given at 1.150″ and for the latter at 1.060″, and charge weights ranging from 4.5 to 5.4 gr. That window is narrow enough to keep folks out of trouble.

    As for the OP, chronographs vary from user to user and brand to brand, and atmospheric conditions affecting air density (like altitude, temperature and even humidity to some degree) will alter velocity measurements. As an example, I have yet to see a Lab Radar record a lower velocity for my 9mm and .45 ACP loads than my dated Chrony, which is a conservatism I appreciate for major matches. However, this powder was designed around race guns using compensators (hence the name), so it wouldn’t be my first choice for general purpose target shooting or competing in divisions where comps are not allowed.

    March 11, 2025 at 8:42 pm #529216
    flyingbrass
    Participant

    I highly recommend using a chronograph when reloading. Flying by the seat of your pants really sucks compared to having data. You don’t have to spend a fortune. A decent optical chrono works fine and provides valuable information. They cost $150ish these days. I consider it a crucial piece of equipment.

    There are multiple factors that will affect velocity even if everything is assembled the same. Moisture content of your powder is a big one. Temperature is another. Plus, you have varying chamber dimensions, throat lengths and angles, bore diameters, case capacities, and so on.

    FWIW, though your results will certainly vary, with Autocomp I got:

    CZ-75 4.7″ barrel
    new RMR brass stamped RMI
    Win SP primer
    124 RMR nuke 1.070″
    4.9 Autocomp
    Temp 77 F
    5 rounds avg 1089 FPS, ES 28

    CZ-75 4.7″ barrel
    new RMR brass stamped RMI
    Win SP primer
    124 RMR nuke 1.070″
    5.1 Autocomp
    Temp 71 F
    5 rounds avg 1118 FPS, ES 30

    S&W Shield Plus 3.1″ barrel
    new RMR brass stamped RMI
    Win SP primer
    124 RMR nuke 1.070″
    4.9 Autocomp
    Temp 77 F
    5 rounds avg 984 FPS, ES 32

    S&W Shield Plus 3.1″ barrel
    new RMR brass stamped RMI
    Win SP primer
    124 RMR nuke 1.070″
    5.1 Autocomp
    Temp 72F
    5 rounds avg 1022 FPS, ES 26

    8 rounds of factory standard pressure Federal 124 HST from the same Shield Plus fired at higher elevation at 73 F averaged 1004 FPS with an ES of 17.

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