my trek to build some 300blackout loads

Discussion in 'Ammunition & Reloading' started by ConcreteJungle, Sep 14, 2015.

  1. ConcreteJungle

    Well-Known Member

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    So I've been playing with some 300blackout loads recently.
    I had multiple goals when I started this build...
    -find out if it can be used as a hunting round
    -build a sub-sonic round with some punch
    -create some plinking rounds
    *these rounds are being fired out of an AR platform rifle, 16" barrel with 1:7 twist, carbine length gas system and auto BCG.

    #1 -
    GOAL: this was intended to be a subsonic round (the plan is to obtain a suppressor down the line)
    *i realize the suppressor will give me different data, but i wanted to start out with a base subsonic load and then build from there.

    Nosler 200gr Accubond
    10.5 grains of IMR 4227
    CCI SRP #400
    2.250 overall length

    PROJECTION: 1100 fps, 537 ft/lb

    -average velocity was 1194 fps
    -based on the ballistic calc this round produces 633 ft/lb of energy

    -Failure...runs too fast to be subsonic
    -Failure...this did not cycle the bolt enough to chamber a new round but it did push the bolt back far enough to eject the spent case.
    -recoil was very light
    The plan is to lower the powder charge and try seating the bullet further into the case...will be going after a 2.220 length in hopes of increasing the pressure a bit so it cycles reliably.

    #2 -
    GOAL: this was intended to be a hunting round/plinking round

    Hornady 165gr SST
    13.5 grains of IMR 4227
    CCI SRP #400
    2.216 overall length

    PROJECTION: 1550 fps, 880 ft/lb

    -average velocity was 1548 fps
    -based on the ballistic calc this round produces 878 ft/lb of energy

    -rounds cycled flawlessly
    -projected data matches the actual data almost identically (very happy about this)
    -good for plinking
    Planning on increasing the powder to get more FPS as this doesn't have enough velocity to give good expansion of the projectile. Next round...16 grains of powder.

    I'll be tweaking the formula a bit for the subsonic round and if I can't get enough FPS out of the hunting round I'll be replacing the 165 grain projectile with a new lighter projectile. The new projectile that will be added to the mix will be in the 147-150 grain variety. I like the Hornady SST bullet so I may stick with that or find a good soft point.
    I'll update this thread as time goes.
    Last edited: Sep 14, 2015
    oli700 and Dyjital like this.

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