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Thread: Neck Sizing a Heavy Straight-wall Case to a Bottleneck

  1. #1
    Join Date
    Aug 2008
    Location
    Illinois
    Posts
    137

    Smile Neck Sizing a Heavy Straight-wall Case to a Bottleneck

    Greetings fellow shooters,

    I am building a new wildcat cartridge based on the needs of a local set of hunting restrictions that apply to me. In other words, it is out of necessity that I build the cartridge, and therefore the cartridge design is something which is maybe a bit of an oddball by the more common standards for wildcat cartridge designs.

    In an effort not to ramble on about why I am using the parent case that I am using, etc, I will simply state the pertinent details. I'm hoping I can potentially get a little help towards obtaining a set of standards to follow, when taking a straight-wall case, shortening the case, and then bottlenecking it down. When I say, "a set of standards", an example would be, how much sizing to do per step (with each new die), I.E., Is there a ratio to follow based on case wall thickness, or diameter, so that I do not try to squeeze too much diameter down per sizing step? Another question would be, how many steps between annealing stages?

    I am going from a case which is 0.635" OD and straight, down to about 0.330" neck, for .30 cal. So it's quite a large transition, which I don't expect to be easy to do without a proper process.

    I am turning the dies myself from grade-5 bolts, since it machines quite well.

    When making the neck sizing dies, are there any rules to follow about an entry cone shape/angle/size? Obviously I would make a shoulder bump die that gets run last, to create the final shoulder angle, I'm just wondering how I should properly prep for that angle bump during the neck sizing stages.

    The neck is going to end up being very short, with a steep shoulder angle alpha of 45.

    I suppose my final question would be concerning prepping the brass wall thickness before neck and shoulder sizing; if I'm starting from brass which has been fire-formed straight, and I indicate off of the outside to ensure each case is centered, can I inside turn the brass thickness down past the entire shoulder to thin it a little in order to aid the sizing process? Or is that a no-no?

    Sorry for all my questions. It's a new process for me, and I would just like to know that I will be setting the project up correctly from the start. Thanks for any help that any of you can offer.

  2. #2
    Join Date
    Dec 2003
    Location
    washington.........STATE that is.
    Posts
    11,921
    Please NEVER be sorry for questions! "There Is Only ONE Dumb Question"

    I do a lot of these and prefer not to go clear down from straightwall, instead trying to find a case that's within 30-40 thou.

    I've recently premiered a bunch of case based on the .404 Jeffery for instance..... started with a .270 (which I made from 7MM RUM, squinched down) followed by .300 and .338 versions (which I blew up) during the course of these developments I tried 3 times to neck down from .404 and failed each time.

    Necking down is hard...... IME you get ONE squeeze of maybe .020-.030 between annealings. I've done as much as .040 with NEW brass and home-aid dies. Different brands of brass yield different results.

    I like Lapua

  3. #3
    Join Date
    Dec 2003
    Location
    washington.........STATE that is.
    Posts
    11,921
    BTW several fellers on here have made and sold dies made specifically for this purpose..... maybe you'll get some real help

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