RCBS X-DIE Full length resizing die???

Discussion in 'The Ammo & Reloading Forum' started by LDBennett, Jul 18, 2008.

  1. LDBennett

    LDBennett Well-Known Member

    Dec 20, 2003
    Hesperia, CA
    Anyone familiar with the RCBS X-Die full length resizer die and its usage?

    It is suppose to eliminate the need to trim brass after firings. Supposedly you must trim once and after that brass is kept from flowing into the neck of the case by the close fit of the neck mandrill and the area of the die that controls the outside of the neck of the case. But the literature most certainly is not clear as to exactly how it is used, at least to me. It raises several questions to me:

    1) The first trimming is suppose to be 0.020 inches shorter than max. Normally brass is trimmed to 0.010 inches shorter than the max. Which is it and why?

    2) Can once or twice or thrice fired brass simple be trimmed and used with the X-Die and brass growth stops? Or must you start with new brass?

    3) How effective is this X-Die? Does it really work as advertised?

    4) Are there any "undocumented features" or unintended consequences from the use of the X-Die?

    5) Is one better served by a standard full length resizing die and regular trimmings?

    This is for use in a semi-auto 308 FAL rifle where full length sizing is mandatory every reload or Failures to Feed may result if the cases are too large and only full length sizing assures no Failures to Feed.

    I would prefer a user of the X-Die with experience in its use and maladies to respond or someone who has read a test report by a reputable source and can point me to that source.

    Thank you,

  2. BigJakeJ1s

    BigJakeJ1s Member

    Oct 12, 2007
    I don't have one, but from what I understand, there is a step in the mandrel corresponding with max case length. That step fills the gap between the die neck and the mandrel, keeping brass from extending past it. I have heard that some users start getting donuts around the base of the neck/top of the shoulder, but that they don't become a problem until the brass is past its useful life anyway.

    Maybe someone who has one can chime in here?


  3. Millwright

    Millwright Well-Known Member

    Jun 30, 2005
    Sorry, can't help with actual experience. I've looked at the "X" die and wondered about two things:

    1. Where does the brass go ? Working brass means there's gonna be some metal moved -somewhere. One consequence I anticipate would be thickening of neck walls.

    2. Another, already mentioned, is into the shoulder and shoulder/neck junction. >MW
  4. 312shooter

    312shooter Well-Known Member

    Mar 17, 2008
    Las Vegas NV
    Gents, just my two cents....I have been using the .308 small base FL X-die and also the redding standard base FL die in .308 for about a year. I decided after a little experiment in resizing 100 rds on each die and comparing them that the X-die theory is only that.....a theory, the slight growth gained from resizing was absolutely equal in both dies, even after firing and resizing a few times as the X-die instructions suggest. The X-die mandrel depth must be spot on or the case mouth misses the step completely or blows out the shoulder - this "tolerance" has turned out to be a very nettlesome setup, I'm still a little green in the reloading world but I cannot find a sensible way to "tweak" the mandrel in .001 increments while its inside the actual die! I have Pics of the X-die mandrel next to a redding, Email - MK10640LV@COX.NET and I'll fire em to you.
  5. LDBennett

    LDBennett Well-Known Member

    Dec 20, 2003
    Hesperia, CA
    I now understand how they work from a google search of other forums since posting this question but I still have other questions.

    The concept is that the case neck is tightly fitted between the de-primer mandrel and the inside of the sizing die and the case growth is stopped by a step on the mandrel. So you start with a trimmed case (0.010 or 0.020 shorter than max??? and must it be only be once fired ???) and it will never grow much more than the initial first firing after the first use of the die. It should never require trimming again in the life of the brass.

    One guy there did a test on ten Lake City 308 Win. cases. He got more than 12 reloadings and the brass was still good. At 15 he concluded the test because he was starting to see problems of case separations in some of the cases. But they went 12 reloadings without a measureable problem. The case length growth stopped after three reloadings but never required trimming. The case thickened in the necks after the 12 reloading but were still reloadable. He normally got only three to five reloadings out of these same cases using regular dies and shooting them in the same gun. There was no accuracy degradation either.

    His testing was very scientific and controlled and worth the read:

    The fourth response.

    This has prompted me to try the X-dies and I can only hope the directions packed with the dies answers all my other questions.

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