Hornady Comparator & Modified Cases
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  1. #1
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    Dec 2018
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    Hornady Comparator & Modified Cases

    Is there an advantage to making modified cases from brass that has been fire formed and resized to the correct headspace as opposed to using the Hornady factory modified case? My local smith says no, that both the factory modified case and the rifle chamber are made to SAAMI spec and it will work. I agree, it will work, but I don't think all chambers are cut identical and the modified cases may also not be the same. That said, I don't see how the base CBTO will be the same if the distance from the lands measured using one case will be the same if the modified case with a different shoulder bump was used to take the initial measurement.
    As of right now, my process is to size the case so that the bolt just closes with no resistance, measure it with a RCBS precision mic and adjust the shoulder setback using a Whidden micrometer locking ring on the die.I'm thinking that once I have fireformed cases and can get a chamber measurement, I can adjust shoulder bump using the adjustable lock ring and the Hornady gauge becomes irrelevant.
    Easy to understand(not rocket science) explanations would really be appreciated.
    Bitter Gun Owner
    Bitter Clinger
    Armed Infidel

  2. #2
    Senior Member Doom's Avatar
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    I assume you are using the OAL gauge. I guess the short answer is you will get a different dimension but the key here is to use the same piece of brass every time. If you were to use your fired brass and take the measurement, then set the shoulder back 0.001” the CBTO should be 0.001” shorter and the bullet deeper in the case by that amount.
    "If we open a quarrel between the past and the present we shall find that we have lost the future.”
    Winston Churchill

  3. #3
    Senior Member ssmods's Avatar
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    Dec 2015
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    I have never been that anal about it. The oal has been measured and I just ran with that. Groups are good enough for just about anyone I know. If you want to go that route you could also just put enough neck tension on a fired case and close the bolt with desired bullet without even using your hornady or stoney point gauge. Should net you the same results without tapping it

    Sent from my SM-G930P using Tapatalk

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  5. #4
    Senior Member rkittine's Avatar
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    All of my precision rifles have custom Whidden dies made for them. You are correct that even factory rifles may have variations from chamber to chamber even from the same reamer and I am not sure a high production rifle is made using only one reamer. They are probably reaming barrels with multiple ones, especially in the same caliber. So, yes to SAAMI specs as close as possible.

    With every new rifle or barrel, I fire 5 cases each three times with not resizing of the body (I use my Wilson Dies and an Arbor press for that) and then send the cases and the reamer print, if I have it, which I do for all my custom rigs, to Whidden for a set of custom dies. Of course if you rebarrel and do not use the same reamer, you may need a new body die.

    I am extremely anal about my cases, my projectiles and all the other components and process loading, but then I shoot at 1,000 yards.

    Bob
    Robert Kittine
    Sag Harbor and Manhattan, New York


 

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