Concentricity woes

Discussion in 'Reloading' started by Ragnarnar, Oct 10, 2018.

  1. Ragnarnar

    Ragnarnar Well-Known Member

    Messages:
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    Oct 6, 2016
    I’m having difficulty eliminating runout in the sizing process of my 7mm LRM. Normally I’m able to achieve sub one thousandth runout in my sizing operation on all my other cartridges fairly consistently, but this one has me stymied. I’ve gone down a couple different paths trying to figure it out but to no avail. I’d appreciate some input or suggestions if anyone has them.

    The rifle in question is a custom job, built with a benchmark barrel and lone peak action. The chamber is cut for the 195 Berger with a .323 to .3224 tapered neck. It shoots 180 VLDs like an absolute laser beam. Fired Hornady 7LRM brass comes out of the chamber measuring around .320+/- OD and with around 1-1.5 thou of runout.

    The brass at this point is annealed on an AMP machine.

    To begin I attempted to size with the die as provided by whidden (.309 neck), with the expander ball and decapping pin in place. When this provided unsatisfactory runout, I removed the pin and tried again thinking this my be “cocking” the die as it resizes. No dice.
    Next I tried removing the entire expander assembly and tried sizing and expanding on a mandrel in two separate steps. Also no dice.
    Finally I tried playing with the height of the expander ball/stem in the die to see if that made any difference. I was able to get my runout down to 2.5 fairly consistently by setting the ball as high as possible then backing off a little bit.

    At this point I began to suspect the brass as the culprit. From the factory the untouched brass has a good deal of thickness variation (high 13s to high 15s) so I broke out the turning setup and skim cut one batch of brass 50% and another batch 90% to see if I was seeing material variations on the runout gauge. After two cycles firing and sizing these two
    batches of this brass I’m still not able to get the runout below 2 thou consistently.

    At this point I have two working theories. One, the die came to me crooked and it needs to go back to whidden to get reworked. Or two, I’m oversizing brass, and thus introducing the runout by kinking the brass necks. I’m leaning option one because I consistently have some runout. If it gave me a no runout piece occasionally I would know the die was straight.

    Thanks for the input.

    TL;DR
    cant eliminate the last 2.5 or so runout from my sizing process.
    Coax press, whidden custom dies, Hornady 7LRM brass, custom rifle.