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Question about Ackley Improved Cartridges

Horse Plains DrifterHorse Plains Drifter Forums Admins, Member, Moderator Posts: 39,309 ***** Forums Admin
edited December 2018 in Ask the Experts
I was looking at loads for a 30-06 AI. One load I saw was 66.0 grains of Reloader 19 under a 165 gr bullet. With these heftier powder charges, and steeper shoulder angle, will these have magnum throat eroding potential? TIA for any insight.

Comments

  • spiritsspirits Member Posts: 363 ✭✭✭
    edited November -1
    Yes, more burnt powder and gas implies more throat erosion - even if the improved case burns the powder more efficiently.
  • nononsensenononsense Member Posts: 10,928 ✭✭✭✭
    edited November -1
    Horse Plains Drifter,

    Here is an image of the cases made from the .30-06 parent case:

    http%3A%2F%2Fyaffa-cdn.s3.amazonaws.com%2Fyaffadsp%2Fimages%2FdmImage%2FSourceImage%2F.30-06-imp1.jpg

    I am slightly amazed at the load you wrote above since it is apparently over pressure by all the loads I work with. But there is no accountability on the internet since no one source polices reloading data.[:(] Every reloader who wants to achieve internet fame tries to add these questionable loads to the discussion in the attempt to raise their own status to 'expert'.

    With regard to the question "will these have magnum throat eroding potential?" The answer is a tentative maybe... but probably not. Given the weight of the load and being above the pressure threshold for the parent case, there is always the potential for some throat erosion.

    However, part of the design resolution of the Ackley case, especially with the .30-06, we have the benefit of not only the 40 degree shoulder but the significantly longer neck as well. When the primer lights the powder, the plasma generated moves forward in the case but is channeled by the steeper shoulder which has the effect of reflecting (directing) the plasma into the sides of the neck and not into the throat. This has the benefit of protecting the throat, extending it's life.

    This fact is often overshadowed by the desire to see improved velocities from the added case capacity. Reality is that the improved shape increases the range of powders which will work efficiently in the capacity as well as improving the efficiency of the cartridge as a whole.

    Best.
  • yoshmysteryoshmyster Member Posts: 20,979 ✭✭✭✭
    edited November -1
    nononsense - That's interesting about the Ackley case. I wonder if they did the same thing to the .308?
  • nononsensenononsense Member Posts: 10,928 ✭✭✭✭
    edited November -1
    yoshmyster,

    quote:I wonder if they did the same thing to the .308?

    If you mean P.O. Ackley himself, it's unlikely since the .308 Win. has very little to gain from the process except for sharpening the shoulder. It will assist with burn rate and powder selection a little but it's not as noticeable as with other cases with mild shoulder angles and sloping case bodies.

    You can find .308 AI reamers and dies so the process is available.

    Best.
  • tsr1965tsr1965 Member Posts: 8,682 ✭✭
    edited November -1
    Actually there are a few misconceptions about the AI chambers, and operating principles. The most misconstrued one is that you just stick an AI reamer in the factory chamber, and your done...not true in most cases.

    The second place winner, is that since you are giving more powder space, you are going to be running at more/magnum pressures. Loads should never exceed the pressure of the parent cases design.

    Nononsense has the OP's question covered exceptionally well.
  • MobuckMobuck Member Posts: 13,733 ✭✭✭✭
    edited November -1
    "Loads should never exceed the pressure of the parent cases design."

    EXACTLY
    And this is where much of the "improvement" came from. Since very few pressure test results were available, the increased velocities often were simply produced by over loading the cartridge.
    And some of the "improvements" were merely "guestimates" of increased velocity.
  • charliemeyer007charliemeyer007 Member Posts: 6,579 ✭✭✭
    edited November -1
    I can think of some more factors. A larger case might mean you can use a slower powder. That could yield more velocity with less pressure and perhaps a ball powder to help with barrel wear.

    A straighter case, less taper could reduce bolt thrust.

    Not many factory firearms in AI, so a good chance your chamber was cut by someone that actually cares as opposed to just a job - no guarantees Bubba did good work.

    I remember reading that P.O. himself thought the 257 Roberts benefited the most % wise towards the ideal case by his improved design.

    Then there are other things like duplex or even triplex loads and lighting the charge at the base of the bullet OKH style.
  • nononsensenononsense Member Posts: 10,928 ✭✭✭✭
    edited November -1
    quote:Loads should never exceed the pressure of the parent cases design.

    To some extent, this 'truism' is fallacious. While I subscribe to all of the thinking about safe handling and safe reloading, there are certain pieces of that thinking which need to be adjusted even if only slightly.

    Take the ubiquitous 6mm PPC which has been all the rage and nearly the only cartridge fielded by the point blank benchrest crowd. The parent case is the .220 Russian with a suggested operating pressure of 50,000 PSI. Convert the .220 case into the 6mm PPC and voila, every man, women and child shooting this cartridge in competition is running it well past 62,000 PSI.

    Then take one of the all time 1/4 bore favorites, the .250 Savage. Standard pressure is noted as being 52,000 psi but when chambered in modern bolt action rifles instead of the Savage 99, you have the advantage of using higher pressures because of the strength of the operating system.

    These are not the only examples available, either. Improvements in the quality of the steel used to make actions and the switch to the stronger bolt action designs will often see pressures on the rise for some cartridges.

    Best.
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