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Thread: Muzzle volocity change from winter to summer ?

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    Muzzle volocity change from winter to summer ?

    First time playing with subsonics in the 300 blackout SBR 10.5" 1:7 Noveske and TBAC 30p-1 at 900 asl. I developed the load in the winter which was 10.9g of 5744 under a 220 SMK and was running 1060 with a 8 fps spread. Started noticing a crack so I ran them through the chrono today at 1120 with a 9 fps spread.

    Would it be normal to gain 60 fps from 40 to 80 degrees?
    Would it be from the 5744, not sure on it's temperature stability?

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    Sonic Crack's Avatar
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    yes. depending on the powder the fps to temp change can be very significant. Try some TrailBoss or H4198
    THE FEW THE PROUD

    www.shortactioncustoms.com



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    I have temp/velocity changes with Grendel, 300 Win mag, and 5.56. I have very minor changes with 308 because I use Varget.

    Much of the change issue can be solved by changing to a powder that is less temp sensitive.

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    Figured it was the powder, no problems with varget and retumbo. Thanks guys. 60 fps seemed like a lot.