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Thread: How to provide the best cases for a .257 Roberts?

  1. #16
    Join Date
    Jul 2004
    Posts
    78

    Forming .257 Roberts from 7x57mm Mauser brass

    (Does anyone mind much if I bump this old thread? There's already some pertinent content here to preface my question.)

    According to Ken Howell in "Designing and Forming Custom Cartridges For Rifles and Handguns" the .257 Roberts can be formed from 7x57mm Mauser brass, as Ned Roberts did. However he does not specify "RCBS form die" as he usually does, but rather (by that omission) may mean a regular full-length .257 Roberts die will suffice for this process.

    Further, I was surprised to find that, with all the form dies Huntington / RCBS list on their web page, there is no ".257 Roberts from 7x57 Mauser" die listed.

    The question, then: Can the regular full-length .257 Roberts die properly reform 7x57mm brass?

    (Please note: I am not asking for a recommendation for Roberts brass, or asking about the relative merits of reforming vs using manufactured Roberts brass. And no, I haven't called RCBS yet. I prefer to kick it around here first before working up the RCBS food chain.)

  2. #17
    Join Date
    Dec 2004
    Posts
    208

    Forming brass

    I formed 6 Remington brass straight from 7x57 Lapua brass, gave the mouth a hard chamfer, lubed with Lee White sizing wax, eased the handle down on the Full Length sizer, perfect cases.

  3. #18
    Join Date
    Jul 2004
    Posts
    78
    Quote Originally Posted by keithcandler View Post
    I formed 6 Remington brass straight from 7x57 Lapua brass, gave the mouth a hard chamfer, lubed with Lee White sizing wax, eased the handle down on the Full Length sizer, perfect cases.
    Thanks! I have heard the "6mm Rem from .257 Roberts" forming is that easy, but everything I've read about "6mm Rem from 7x57mm" says necks will be too thick and need turning. Also, some had collapsed shoulders and felt a two-stage forming was warranted (e.g. down to .257 Roberts, or at least neck size down to .257 first.)

    So the necks weren't too thick for your 6mm Rem chamber, and no "doughnut"?

    Brian
    Last edited by Brian Adams; 07-17-2014 at 01:27 PM.

  4. #19
    Join Date
    Mar 2003
    Location
    Mercer Island WA USA
    Posts
    212
    I have put Win or Rem 8x57mm brass in a 7x57 Wilson vise die, and from there into a 257 Roberts Wilson vise die.
    No interference from a thick neck and shoots 1/2" 5 shot groups at 100m in a 257RAI on no wind days.

    But if I neck down Norma 7x57mm rimmed to 257 Roberts and shoot it in the a chamber made with the same reamer as above, I get interference. The chamber neck is 0.288"
    So I turn them on the lathe ala Mike Bryant.
    The rimmed brass, which should be good for much higher pressure than rimless, is soft as butter and cannot even keep up with rimless.

    And the same sort of thing happens when necking down 308 to 260. Different brands wind up with very different thicknesses. The chamber neck in 0.298" and 308 Lapua brass needs to be turned. 90% of Win does not.

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