Muzzle velocity vs barrel length

Discussion in 'The Basics, Starting Out' started by Mc Fraser, Sep 16, 2018.

  1. Mc Fraser

    Mc Fraser Member

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    Hi Everyone,
    I have a Win M70 in 300WM with a 28” Krieger barrel.
    My question is: most of reloading books are based on a 24”in barrel, the 4in difference on my barrel will increase or decrease the muzzle velocity compared to one advertised in the book.
    TIA.
     
  2. Vortex!

    Vortex! Well-Known Member

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    Increase.
     
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  3. Mc Fraser

    Mc Fraser Member

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    Thank you.
    Is there a rule of thumb to determine by how much? In the absence of a chronograph.
     
  4. Vortex!

    Vortex! Well-Known Member

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    I don't know how much for sure but it does increase a little for every extra inch.
     
  5. Vortex!

    Vortex! Well-Known Member

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  6. Vortex!

    Vortex! Well-Known Member

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    In this guy's situation he lost 25 fps for every inch he cut off of the barrel.
     
  7. J E Custom

    J E Custom Well-Known Member

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    In your 300 Win Mag it should be a little faster. smaller cartridges may not benefit from a longer barrel because of the amount of powder they use.

    Normally, the larger the case capacity the greater the gain for each inch of barrel. But there is a nominal barrel length for each cartridge and any more length causes the increase to becomes very small

    J E CUSTOM
     
  8. Bravo 4

    Bravo 4 Well-Known Member

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    It should be faster compared to if that same barrel was shorter, however it may not be faster than another rifle's 24 or 26" barrel. What I mean is that some barrels are faster than others, or slower.
    Couple examples:
    I had a factory 7mm RemMag Savage 112 with a 26" barrel that had a slow barrel, I could only get the 162 and 168 grain bullets up to velocity that most .280's would get.
    My last 26" .338 RUM barrel would reach the same velocities as my 30" .338 Edge.
     
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  9. Mc Fraser

    Mc Fraser Member

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    Thank you this is realy great information.
     
  10. Weatherby Fan

    Weatherby Fan Well-Known Member

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    As Bravo 4 pointed out every rifle is different, my brother and I have identical Mark V SS 300 Wbys 26” barrels and with factory ammo out of the same box which is advertised at 3240 FPS his rifle shoots it at 3280 FPS and mine won’t shoot it over 3200 FPS,
    So there’s 80 FPS difference in the same 26” length barrel,
    In theory you 28” barrel with a magnum cartridge should benefit but I notice in my 28” 6.5 CM it’s the same speed as my 22” CM ?
     
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  11. djm670

    djm670 Well-Known Member

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    There have been a couple of tests on a 6.5 creedmoor but I can only find the following one on a 300WM

    https://rifleshooter.com/2013/12/30...rrel-length-change-velocity-a-16-300-win-mag/

    And the maximum length barrel in this one is a 24.25" my guess is that longer barrel on a the larger diameter .300WM such as your 28" barrel is significant.

    Each reduction in barrel length averaged 39.6 ft/sec in velocity loss. Significant jumps in velocity reduction occurred between 18.25 and 16.25 inches (56, 65 ft/sec) and between 23.25 and 22.25 inches (65 ft/sec). Standard deviation generally decreased as the barrel got shorter.

    [​IMG]
     
  12. B-LOT Banga

    B-LOT Banga Member LRH Team Member

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    Can the twist rate affect the Bullets speed (FPS)? For instance all being equal except the twist rate... would the bullet of a 1-9.5” twist be faster (FPS) than a 1-8” twist because of less resistance with the rifling trying to get the bullet to spin faster?
     
  13. manitou

    manitou Well-Known Member

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    Yes... twist rate will affect speed.
     
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