Effect of barrel length on load data???

Discussion in 'Reloading' started by gbraach, Jan 21, 2008.

  1. gbraach

    gbraach Member

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    In general, what effect does a different barrel length have on published load data. For example, I am looking at published load data that was developed using a 26" barrel. My new rifle has a 30" inch barrel.

    Can I increase the amount of powder used?
    Should I use a faster powder? a slower powder?

    Thanks in advance for any help!
     
  2. dirtball

    dirtball Well-Known Member

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    The longer barrel length should have NO effect on your "published load data" You will probably get a little more velocity with the extra barrel length. By NO means use "More Powder", with out starting low and working up. It is possible depending on the cartridge that going to a slightly slower burning powder would get a few more FPS without increasing pressure since you have more barrel in which to burn the powder.
    Stay with the minimum or "Starting loads" until you know how your rifle reacts to them, variations in chamber size, case capacity among things can result in very bad things happening if you start with a heavy or max load.
    Dave
     

  3. gbraach

    gbraach Member

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    Thanks DirtBall. I appreciate your response.

    But it doesn't quite answer what I am trying to learn. I am just trying to determine what effect a longer barrel or for that matter a shorter barrel has on any given load.

    Let me try asking in a different way.

    According to my reloading manual the starting load for my hypothetical cartridge is 42 gr. of Brand X powder which results in a velocity of 2800 ft. The published reloading data is based on a 26" barrel.

    What would be the differences if I used the exact same starting load in the same test rifle but now it has a 30" barrel? Would pressures be higher or lower? Would velocity be higher or lower? Any other differences?

    Thanks
     
  4. dirtball

    dirtball Well-Known Member

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    ALL things being equal the extra 4" of barrel will not affect pressure. Peak pressure in most bottle neck rifle cartridges will occur in the first 6-8" of the barrel. What the additional 4" does give you is more time for the pressure in the barrel to accelerate the bullet therefore resulting in more muzzle velocity, in something like a 30-06 probably 100 to 150 fps.

    Dave
     
  5. Mikecr

    Mikecr Well-Known Member

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    Published loads are based on pressure. YOUR loads are based on pressure AND accuracy.
    Barrel length will not affect pressure of concern(as mentioned). But because your barrel will produce an extra 100fps or so of muzzle velocity, and the muzzle will be in a different place on bullet release, your most accurate load might be anywhere.

    Treat the barrel no differently.
    Good luck
     
  6. badaboom

    badaboom Well-Known Member

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    Good answers but what a oxi-moron "your most accurate load might be anywhere."
     
  7. 338hammer

    338hammer Well-Known Member

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    Barrel legth

    Just trying to answer what I am thinking the answer requested.

    My 24" 338 Gibbs shoots a 180grain Accubond at 3100fps
    My 17" 338 Gibbs shoots the same bullet with the same load at 2800fps+
    divide 7 (barrel lenght difference)into 300fps viarience and that will tell you for this cartridge anyway what the lost of velocity per inch is. It also works in reverse.

    Understand every caliber,barrel and bullet weight and in particular powder, will be different under the above formula. I always use 30fps per inch as a rough base of expectation.

    338
     
  8. indiansumer

    indiansumer New Member

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    "your most accurate load might be anywhere." or.....you might find your most accurate load to be anywhere in the velocity ranges you are achieving. Meaning the pressure is not the factor in accuracy but instead the speed of your bullet as it exits the muzzle which, at the same pressure, can vary with barrel length. Better?
     
    Last edited: Jan 26, 2008