.280 Ackley Improved build questions

Discussion in 'Gunsmithing' started by fj40mojo, Apr 21, 2011.

  1. fj40mojo

    fj40mojo Well-Known Member

    Messages:
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    Jul 25, 2009
    Here are the specs:
    FN Mauser 98 Action
    Krieger #3 Sporter Contour 1:9 .284/7mm @26"
    B&C Medalist Varmint stock
    Tubbs Speedlock firing pin and spring
    Timney Featherweight Trigger
    EGW 20 MOA Rail
    IOR Valdata 10X with MP8 reticle

    Plan:
    160-180grn bullets from Norma fireformed brass

    Here's the questions:
    #1. Can anybody tell me the average neck thickness of Norma .280 brass? I am considering having a custom reamer made and want to know so I can calculate optimum neck diameter and not have to neck turn.

    #2. Can I cut a custom sizing die with the same reamer used to cut my chamber? I plan on building a bushing type die so basically all the die would be doing is bumping the shoulder and mild body sizing. Bushings would be purchased not built.

    #3. I need some dimensions from the 7mm 180grn Berger Hunting VLD-length from base to Ogive and Overall length to calculate throat and COAL.

    Thanks in advance for the help.
     
  2. shortgrass

    shortgrass Well-Known Member

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    Mar 31, 2010
    The best way to get the reamer you want is to buy that Norma brass and a box of those Berger bullets and assemble 1/2 dozen or so and ask your tool maker how many he would like for samples to grind the reamer to. Chambering reamers don't make good sizing die reamers. When you re-size a case it needs to be slightly smaller than the chamber for ease of chambering a round. If this is a hunting rifle, and I assume it will be with a #3 contour barrel, don't get the neck too tight. You might consider using Nosler .280 A.I. brass as it's already formed to A.I. which would eliminate just on more variable that fire-forming will introduce. If ya' build a rifle with a tight necked chamber, make sure you mark the neck diameter on the barrel along with the caliber.
     
    Last edited: Apr 22, 2011

  3. J E Custom

    J E Custom Well-Known Member

    Messages:
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    Jul 29, 2004
    I would recommend using a standard 280 AI reamer from Manson or PT&G. It is not easy to get
    a special reamer correct and the problems can be devastating.

    It is easy to turn the neck If it is to tight (.003 thousandths larger than a loaded round is my
    minimum clearance.

    If chambered and head spaced correctly there is little or no improvement in accuracy .

    Tight tolerances should be approached with caution.

    Fit the case to the chamber not the chamber to the case. This leaves you with many options
    and some flexibility.

    Just my opinion for what it's worth.

    J E CUSTOM
     
  4. fj40mojo

    fj40mojo Well-Known Member

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    392
    Joined:
    Jul 25, 2009
    Thanks.