Improved case limits

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by Ozyboarhunter, Oct 1, 2011.

  1. Ozyboarhunter

    Ozyboarhunter Member

    Jun 12, 2011
    gday all does anyone know what actual min taper is and max shouulder angle is etc?

    or where i can get info on this topic?

    going to improve some cals and draw them up get reamers made

    any help is good help


  2. MagnumManiac

    MagnumManiac Well-Known Member

    Feb 25, 2008
    G'day fellow Aussie!

    I can't tell you where to get published info, other than P.O.Ackley's books, but I can tell you what I know.

    A 45 degree shoulder is said to be the maximum angle, it's also said to be the closest to a radii shoulder like the Weatherby mags.
    A 40 degree shoulder is said to be the most efficient.
    Although the new 'beltless' magnums have not used this angle, they use 35 degrees, this angle is preferred, but it can and does cause feeding issues in some actions.
    Minimum case taper can be run at .010", but somewhere in between .010"-.020" is desirable.

    Have a look at any info you can find on the "Gibbs" line of wildcats, they use minimum case taper and sharp shoulders moved well forward than the original position of the 30-06 case they are based on.

    Hope this helps you out.

  3. J E Custom

    J E Custom Well-Known Member

    Jul 29, 2004
    P O Ackley did a lot of testing and recomended a minimum of .007 thousandths Per inch.
    I normally stop at .009 to ease ejection.

    As far as shoulder taper= again, Ackley recomended 40o max. and again being conservative
    I like 37.5. There is almost no gain going to 40o and feeding is not a problem with 37.5 degrees.

    On smaller diameter cases (3006 and down) 40 degrees seems to work fine. where feeding
    starts to become an issue is with the magnum and larger cases unless provision are made
    to the breach.

    So I would say that the limit on both would be 40 degrees and .007 thousandths per inch body

    One way to increase powder volume/capacity is to move the neck shoulder junction forward.
    the minimum for small diameter bores (22 to 7mm) is one caliber in length.

    On larger calibers (.308+) you can get buy with less because of the surface contact with the
    bullet. A good example is the 300 win mag .308 bullet diameter and a neck length of .264.

    So if I want to increase case capacity I blow the body out to .009 thou per inch and make
    the shoulder angle 37.5 to 40 degrees and then move the shoulder forward the max possible
    based on caliber and this gives me the maximum capacity of the case . I just wildcat-ed a 375
    RUM to 338 and increased powder capacity between 10 and 15 grains without a drop tube
    depending on the type of powder.

    I hope this gives you something to think about.

  4. Mikecr

    Mikecr Well-Known Member

    Aug 10, 2003
    For true single shots(like TCs), there are JDJ cartridges with shoulders up around 60degs. And somebody around has just developed a pretty radical radiused shoulder(even moreso than weatherby). I would be good with ~40degs for a single shot bolt action. Also 10thou max per inch body taper.
    I also subscribe to WSM ratios, as patented, and 6PPC flamepoints for the necks.

    Good reading on the subject:
    "Designing and Forming Custom Cartridges" Book by Ken Howell - MidwayUSA cartridges of the world: Books
  5. Rocky Mountain

    Rocky Mountain Well-Known Member

    Sep 13, 2010
    It depends on the diameter and length of the case to what taper per inch is best.
    I've used 6 thou per inch on a .473 diameter 2.5 inch total case length with good results.
    In a .532 diameter case 2.5 long 7-7.5 thou per inch has worked well.
    In a .585 diameter case 2.7 to 2.9 inches long 7.5 to 8 thou per inch has worked well.
    In a .640 diameter case 3.043 long 8.5 to 9 thou per inch has worked well.
    hope this helps.
  6. Ozyboarhunter

    Ozyboarhunter Member

    Jun 12, 2011
    thx a lot men, all have been help full

    the Ken howell book has been dis continued .. anybody want to sell one? :)
    Last edited: Oct 4, 2011
  7. Mikecr

    Mikecr Well-Known Member

    Aug 10, 2003