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

  1. #1
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    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
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    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
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    BTW several fellers on here have made and sold dies made specifically for this purpose..... maybe you'll get some real help

  4. #4
    Join Date
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    Quote Originally Posted by alinwa View Post
    BTW several fellers on here have made and sold dies made specifically for this purpose..... maybe you'll get some real help
    I think the largest neck down I've done was forming a 7MM Alpo from a 444 Marlin case. I used a 35 Rem, 308 and 280 Remington AI shortened. It was for a Contender and the 280 die was shortened so that a factory round wouldn't chamber. Skip Otto made form dies for such a project, but I believe mine came from PBIKE (Paul Becignuel, sp?). Paul's dad Francis reads this forum from time to time, but since he and Al don't quite gee haw, he make not look at this thread. I'll give him a head's up and maybe he'll post. I've used Paul's form dies to remake 6 BR brass (prairie dog) from well used 30 BR. Worked pretty well.

    Rick

  5. #5
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    Poetry, Tex.
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    I used to make and sell case forming dies. I have reduced 458 Lott to 224. Needs to be in steps of .030. Don't worry about shoulder angle as your fireforming will take care of it.

  6. #6
    Join Date
    Feb 2006
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    168

    wildcat

    Mirage -

    My custom RCBS case forming die set for my " .22-35 Remington " wildcat featured 3 neck-down steps.
    .358" to .308" cal, .308" to .257" cal; and then .257" cal to .224" final cal. That's a .050" redux, followed by a .051"; and then a .033" redux.
    That's how RCBS set up the forming die steps, and I did not do any annealing of the new parent brass efore performing the 3 neck-down steps.
    The form set also included an inside neck ream die + reamer. My final desired neck wall thickness for the wildcat was .010", and I only had to do a veryminor amount of outside neck turn to uniform things.

    Whenever / wherever possible, I like to do wildcat case forming using existing ( usually FL sizer ) dies. When this is the approach used, one would likley be utlilizing
    dies for the more common calibres, and nothing exotic.

    Thinking out load in loose terms.... an example neck-down process might be: .620" down to .585" cal, .585 - 550", .550 - .500", .500 - .452", .452 - 416", .416 - .366";
    and likely then a final step of .366" cal down to final .308" calibre. While this last step is a neck-down of .058" ( more than the .050" redux proposed in previous steps );
    let's remember that necking down brass several calibres can produce thickened case' neck walls. Therefore, reaching the final .308" cal desired for the wildcat will be a comination of both the final neck-down step + inside neck ream and outside neck turn; to insure final neck wall uiformity. The inside neck ream would be cutting the entire inside neck length. It would not be just cutting out a " doughnut ", especially on fore-shortened brass.

    I'd have to research whether there are any existing dies that could work for your project, especailly whether there are any that could / would work if the die were shortened

    I think of the final 2 inside neck ream and outside neck turn steps as insuring uniformity of the neck walls from a central inside reference point; as you are using mandrels. in the tooling.

    Starting w/ new cases..... I'm not convinced you'd have to due any annealing. Once the shoulder location is set from the first step, and using a shoulder angle that allows for reasonable forming forces ( and no case losses ); then.... basically all the action will take place in the progressive calibre redux steps ( the neck ), along with some small transitions of material into upper shoulder surfaces associated w/ each calibre.

    The final 45* shoulder angle would need to be fire formed, as such angles are too tight to be formed mechanically using traditional steel dies. A hydroform-type die might be a different matter ?


    With regards,
    357Mag

  7. #7
    Join Date
    Feb 2006
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    wildcat

    Mirage _

    Howdy, again !

    As regrards case annealing:
    You can always try form a trial case(s) using the dies chosen for the case forming process. IF / when you see any " striations " in the formed case' shoulders or even worse.... ones that go up into the neck wall; that'd be a pretty good indicator that the brass does need an annealing first.... and also possibly that the shoulder angle featured in the die(s) is too aggressive.


    With regards,
    357Mag

  8. #8
    Join Date
    Jul 2005
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    I would give RCBS a call.
    You might even need to send them a drawing of the chamber.

    They used to be very good at this.
    They have a wide stock of dies that allows them to select multiple steps
    to get the neck down bit by bit (or 'die by die').

    It may require inside reaming or outside turning along the way.

  9. #9
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    ROCK ON Guys!!!

    Keep 'er coming.....

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