Ackley Improved vs Parent Case

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by BRIT, Mar 26, 2012.

  1. BRIT

    BRIT Well-Known Member

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    Gents.
    Could you please help with a question i have been thinking about please?
    Does using the Ackley Case result in less pressure than the parent case when giving identical performance?
    For example.. Does a 25-06 AI using H4831 propelling a 100 grain bullet to 3200fps develop less pressure than a standard 25-06 using same powder and bullet to same velocity? Everything else being equal also.
    Many thanks for any thoughts you could offer on this.
    Has there been any pressure testing been done on this?

    Brit.
     
  2. ZSteinle

    ZSteinle Well-Known Member

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    Yes. More case capicty will lower pressure
     

  3. Mikecr

    Mikecr Well-Known Member

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    The purpose of improving a case, Ackley or otherwise, is not to reduce pressure. It's actually to allow higher pressures than the parent case would(and survive for many reloadings).
    With improvement, you change powders to regain load density and outright gain velocity.
     
  4. BRIT

    BRIT Well-Known Member

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    ZSteinle
    Thank you for your answer. This is how i understand it. I am hoping i can get a definitive answer to this.


    MikeCr.
    Thank you for your reply. I agree entirely with everything you say. Can i though most respectfully ask you to consider the question i raised about like for like pressures.
    Many thanks

    BRIT.
     
  5. J E Custom

    J E Custom Well-Known Member

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    The main reason to use a ''improved''case is to increase the powder capacity. This allows the use
    of slower burning powder lowering the pressure by volume. when you go to slower powder you
    can add more to reach the same pressure with more volume of gas increasing the velocity.

    With a short barrel there is no real advantage but when you increase the volume it is advantages
    to use a longer barrel to help consume the slower powder.

    So theoretically if all things are equal (Pressure, bullet weight, barrel length,twist rate ETC) velocity
    will be very close to the same. and adding barrel length to smaller capacity cases with fast burning
    powder will not get you much gain, but increase the case capacity and the charge of slower burning
    powder along with a longer barrel and the gains will be noticeable.

    J E CUSTOM
     
  6. Mikecr

    Mikecr Well-Known Member

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    As JE implies cartridge design and gun design as a system, is complicated much like engine designing. Any shade tree mechanic can combine parts to make pure junk.
    But that's more abstract than design.

    Cases are improved for much more than capacity, and some improvements are actually designed to reduce capacity(like a 6xc over a 243win) for use of faster powders with given bullets. Most improvements begin with a reamer print, and appropriate reloading plan(case forming, fireforming, sizing, action, barrel, etc, with a specific bullet and powder in mind).

    Brit, to the original question, 'Ackley' improvements do increase capacity, as well as reducing body taper, and increasing shoulder angle.
    And with your example of a standard 25-06REM, H4831, 100gr bullet @ 3200fps:
    -It has an H20 capacity of ~66gr, and your load would be~57gr H831sc from a 26" barrel. This is already a very low pressure load @ ~50Kpsi.

    -Changing only to AI capacity(~71grH20), Pressure drops to ~43Kpsi, and MV drops to ~3070fps.
    Regaining velocity(which you're allowing) means adjusting load to 59.3gr of H4831sc, and this does provide 3200fps @ ~48Kpsi (a 2Kpsi drop in pressure).

    So the answer in this case is YES
     
  7. TOM H

    TOM H Well-Known Member

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    Brit, all you have to do is look at Sierra data for the 25-06/25-06AI they used same rifles same bullet/same powder.

    question
    Does a 25-06 AI using H4831 propelling a 100 grain bullet to 3200fps develop less pressure than a standard 25-06 using same powder and bullet to same velocity? Everything else being equal also.

    According to Sierra in a 25-06AI it takes 55gr/H-4831 with 100gr bullet @ 3200fps

    In a 25-06 it take 53.6gr/H-4831 with 100gr bullet @ 3200fps
     
  8. BRIT

    BRIT Well-Known Member

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    Gents
    A very big thank you to all of you who took the time to answer my post. I genuinely appreciate it.
    Mike Cr.
    Exactly what i was hoping for,thank you

    Brit.