Case Neck Thickness Grows with firing/sizing cycles?

Discussion in 'Reloading Forum (All Calibers)' started by HTSmith, Nov 9, 2019.

  1. HTSmith

    HTSmith Silver $$ Contributor

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    My 6BR rounds that were measuring .268" across the necks are now measuring .270" with the same lot of bullets seated. Is this normal? I'm concerned because my chamber is .271".
     
  2. Dusty Stevens

    Dusty Stevens COVFEFE- Thread Derail Crew Gold $$ Contributor

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    Yes you need to re-turn every firing until they stop
     
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  3. HTSmith

    HTSmith Silver $$ Contributor

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    Dang. That ain't what I wanted to hear;)
     
  4. 243winxb

    243winxb

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    Has brass become thicker at the neck shoulder junction? Donut? Just asking. :)
     
    Last edited: Nov 9, 2019
  5. SPJ

    SPJ Gold $$ Contributor

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    Dusty is normally correct but I’m thinking that carbon is building up inside the necks adding to thickness.
    J
     
  6. David Christian

    David Christian Gold $$ Contributor

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    Brass is flowing from the case side walls to the shoulder and then into the neck. Therefore, you have a thicker loaded round.

    Have you thought about turning 10-20 of them and then conducting a mini test against 10-20 that you left unturned? If you then shoot them round robin, measuring speed and POI on target, might be neat for you to see the difference.
     
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  7. HTSmith

    HTSmith Silver $$ Contributor

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    I always give them one twist with a brass brush before loading, so it leaves a little carbon. I'm measuring just below the case mouth so its not in the doughnut area. Crazy as it sounds I've never neck turned. The new rounds were 268 on a 271 chamber so I figured I was good. Now they've grown. Looks like I'm going to get dragged kicking and screaming into the neck turning world:(
     
  8. Larryh128

    Larryh128

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    Don't kick & scream, neck turning will yield results.
     
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  9. Dusty Stevens

    Dusty Stevens COVFEFE- Thread Derail Crew Gold $$ Contributor

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    Send your barrel to your gunsmith and get the neck reamed out to .273 and just change bushings as you go. They wont get that big. I have a neck reamer just for this reason
     
  10. carlsbad

    carlsbad Lions don't lose sleep over the opinions of sheep. Gold $$ Contributor

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    What tool are you measuring with?

    And you didn't have enough neck clearance in the beginning.
     
  11. HTSmith

    HTSmith Silver $$ Contributor

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    Mike.jpg
     
  12. HTSmith

    HTSmith Silver $$ Contributor

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    How much clearance is enough?
     
  13. Bill Norris

    Bill Norris Silver $$ Contributor

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    .002 is most desired from what I read
     
  14. David Christian

    David Christian Gold $$ Contributor

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    A lot of F-class shooters are striving for more neck clearance these days and have not seen any degradation in their group sizes or scores. I personally target .005 - .006 in all of my barrels across 3 different calibers.
     
  15. SPJ

    SPJ Gold $$ Contributor

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    I had to check to be sure, mines 2685 OD / 272 neck with zero problems to date.
     
  16. dkhunt14

    dkhunt14

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    I use the Mitutoyo from K&M, it has the spindle ground so the contact point is smaller. It gives a much more accurate reading because you are not bridging a big area. It also hard to measure a radius with a wide contact point. Matt
     
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  17. HTSmith

    HTSmith Silver $$ Contributor

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    That makes sense, but for the time being I'll have to use what I have. My calipers give very similar readings. I usually measure in about a half dozen places and get pretty consistent measurements. (BTW the Marvel Mystery Oil works like a champ)
     
  18. dkhunt14

    dkhunt14

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    If you go to K&M website and look at a pic of their micrometer, you will see what I mean. If he grinds them, other people can too. Matt
     
  19. Dusty Stevens

    Dusty Stevens COVFEFE- Thread Derail Crew Gold $$ Contributor

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    Hollands sells a very nice tube mic. @dkhunt14 i think hes measuring over a loaded round with his calipers
     
  20. JimSC

    JimSC

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    Just got my first 6 BR and I found that the lot of Lapua brass (lot # 4PH6046) would chamber first firing but after resizing was too thick at about .015 in the neck. Norma (lot # 10260157) brass measured .012 thick in the neck area and on the second firing has required no turning.
     

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