Barrel length and velocity?

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by KiloTango, Apr 5, 2013.

  1. KiloTango

    KiloTango Active Member

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    At what point do you start seeing diminishing returns on velocity gains with respect to barrel length with a 6.5x47? Need to make a decision on barrel length, hoping to get good velocity but not wanting an excessively long barrel that doesn't gain me any appreciable velocity.
    Thanks,
    Ken
     
  2. J E Custom

    J E Custom Well-Known Member

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    Small volume cases need less barrel length to perform near there potential max velocity.

    The larger the case volume and the heavier the bullet the more barrel you need.

    For the 6.5x 47 24" is about ideal. 26" would about max. more barrel than 26" is in this category
    (Less gain per inch).

    J E CUSTOM
     

  3. KiloTango

    KiloTango Active Member

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    Thanks.
    Ken
     
  4. MontanaRifleman

    MontanaRifleman Well-Known Member

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    Also faster burning powders require less barrel length than slower burning barrels for greater efficiency.
     
  5. aramarine6

    aramarine6 Well-Known Member

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    Glad you pointed out CASE VOLUME and not CASE LENGTH. Some believe that a "short action" doesn't need a long barrel. However a WSM case would be optimized in 26+ inch barrels. Just remember the further you get away from the chamber the velocity increase will become less and less with each inch added. I'd agree that a 26 inch barrel would be the longest you'd want to go before the gains in velocity arent worth the added length and weight.
     
  6. jason frazier

    jason frazier Member

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    I shoot a custom 6mm rem. It has a 1:8 twist medium varmit barrel,26 inch. if i could have put a heavier barrel on it i would have, but i was limited by the stock. I think If I was to start from scratch. I would go with a heavier barrel, but leave it at 24". just not burning that much powder, plus faster powders are better in the 6.5x47
     
  7. Bart B

    Bart B Well-Known Member

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    In the SAAMI tests with barrels from 22 to over 30 inches and bullets in the 2500 to 3000 fps range, muzzle velocity increased about 25 to 30 fps per inch of increased length. SAAMI's web site has documents on centerfire rifle cartridges documenting this.

    Unless the barrels one uses to compare muzzle velocity have the exact chamber, bore and groove dimensions as well as firing pin and ammunition properties, the velocity numbers for each length will not be good for comparison.

    Exactly how does one measure or calculate the "efficiency" of a load for a given barrel?
     
  8. J E Custom

    J E Custom Well-Known Member

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    Dan Lilja did a test that involved starting with a 46" barrel and cutting the barrel 2 inches shorter
    and re crowning after each test.

    It is a very good article and well worth reading. Log on to his web site and find it in "Articles".

    It shows the relationship with velocity and barrel length and the deference in short barrels and
    long barrels also.

    I don,t know if there is a good way to measure efficiency of any load except if it is consistently
    faster or shows less pressure than listed loads. Also some barrels are a little faster than others
    with the same loading and may skew any efficiency test.

    For years I had heard that short fat cases were more efficient than longer cartridges with less body diameter. and when comparing a 7 WSM to a 7 rem mag I found that it took the same or less powder in the 7 rem mag to achieve the same velocity with the same bullet weight Even though
    the effective barrel length in the 7 rem mag was shorter because the case is longer with the same overall barrel length.

    The powder and primers were the same in both rifles.

    As you said there are so many variables that I don,t think there is any way to accurately measure
    efficiency.

    Just my opinion.

    J E CUSTOM
     
  9. aramarine6

    aramarine6 Well-Known Member

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    I bought the Cartridge Comparison Guide by Chaimberlain Development. It shows cartridge effciency using the muzzle energy divided by the powder weight recquired. It gives most cartridges an efficiency between .40-.60 However all this information is generated from various different reloading guides and doest state barrel length for each given load. Regardless its a pretty interesting book.