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Do barrel extensions affect muzzle velocity?

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  • Anangrypasta

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    Might be a silly question, but do thread on barrel extensions affect muzzle velocity? Been interested in picking up a 9mm rifle with 16 inch total length "barrel," but it's actually a 5.5 inch barrel with a 10.5 pinned extension (the idea is to reduce the weight and change balance of the gun but make it rifle length). Does anyone have insight? I know 9mm isn't too shabby out of a longer barrel, the government said it's capable of blowing something.
     

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    Anangrypasta

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    I should add, it's a competition 9mm rifle so terminal performance isn't really that important. Mostly asking out of total curiosity. If there is some sort of velocity benefit, I guess there would be aftermarket adds so you could slap one on a Glock or something.
     

    fir

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    It should provide some freebore boost, but that apparently is dependent on the heat of the barrel extension or suppressor after shooting consecutive shots.


    To be clear, that article is pointing out that the freebore boost is entirely dependent on the heat of the suppressor. What is happening is that the suppressor or shroud is creating a hot, low pressure zone that the bullet will travel through more easily after uncorking (and can also facilitate more complete burn of unburnt powder). The difference in his testing for 223 with a suppressor will not translate to 9mm with a hot shroud. Though the shroud will still create a low pressure area when it heats up.
     
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