6.5 Creedmoor headspace numbers

Discussion in 'Big Stuff--7mm, 30 Cal, .338+' started by 4PopCropp, Nov 5, 2017.

  1. 4PopCropp

    4PopCropp

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    I'm installing a Remage barrel in 6.5 Creedmoor. So I've threaded the receiver onto the barrel with the Go Gauge inserted. This should be SAAMI minimum headspace. Then I inserted the No Go gauge and verified the bolt won't close.

    I've read you should then back off the receiver .003 so you're not right at minimum. However, in researching the Creedmoor drawings and taking my own headspace measurements with my Hornady HS gauge and calipers these are the numbers I come up with.

    SAAMI Chamber min HS - 1.541
    SAAMI cartridge min HS - 1.5368
    Manson Go Gauge - 1.533
    Manson No Go Gauge - 1.539
    New unfired Lapua brass - 1.530

    Given these measurements, should I install the barrel at minimum headspace and leave it there? Seems I would have .003 clearance with Lapua brass right there.
     
  2. 243winxb

    243winxb

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    (comparator)
    May not give a true measurement.

    The extra .003" sounds good to me.
     
  3. rardoin

    rardoin Silver $$ Contributor

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    If you have a dedicated source of brass (and not shooting factory ammo) there is no reason to allow your brass to blow out more than 0.002-3". I set my Creedmoor barrels to just close on a Manson go gauge which allowed easy bolt closure on new Lapua brass. My fired brass has been 1.5330-1.5335" at the 0.400" datum after the second firing and I have my die set to produce 1.5320" brass. I have at least 30 firings on some 'formed from .308 Palma' cases and the brass hardly has to be trimmed...maybe every 6th firing. I anneal every loading ans the necks are fine save for a single case that was lost due to a thin spot weakend by neck turning. I would not back off any further than what it takes on the go gauge. For my last barrel I used 3 fired cases....I set the barrel where the bolt had very slight contact on the 'longest one' and torqued it down there. I have used the same brass on the last two barrels.
     
    jdh47 likes this.
  4. 4PopCropp

    4PopCropp

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    Ok, thanks. I think I will follow your advice. It is the direction I was leaning in, but I wanted to know how others have handled headspace. I know my Hornady gauge may not be super accurate, but I figured if I use it to compare the Go and No-Go gauges to the actual brass I intend to use I should have a pretty good idea of the differences between them. Thanks again.
     
  5. Texas10

    Texas10 Gold $$ Contributor

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    It's been my experience that head space gages are a very useful tool for a Gunsmith troubleshooting a customers gun. For you and me, setting our barrels into actions, they're not so useful because the two things that are important to me are;
    1) The new brass I intend to use will chamber easily for fire forming.
    2) The dies I use are set up properly to minimize working the brass at each loading while still getting a good fit to the chamber.

    So for my new 6.5CM, I purchased 100 rounds of Hornaday ammo, measured the base to shoulder on a handful using my Hornaday gage, selected the longest one and pulled it down to use the case as a headspace tool.

    I set the barrel to fit that case, with easy bolt closure. Then to verify, placed two layers of scotch tape on the head and tried to close the bolt again. Wouldn't close without a lot of effort.

    I then shoot the factory loads, fire forming the brass in the process and then set up the FL die to bump the shoulder .002 on the as-fired case that chambered with a slightly stiff bolt closure. Sometimes takes several fire forming cycles to get that maximum case length which I save as a reference.
     
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  6. shoot4fun

    shoot4fun Gold $$ Contributor

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    Not to dispute what you're saying here but I was told by Hornady tech support (and it is also in the Hornady comparator chart) that the correct comparator is "C"/.375 for the 6.5 Creedmoor. On a side note, I would have thought the 6 Creedmoor would be the same but my reamer print from PTG shows it to have a .400 datum.
    I don't have a 6.5 Creedmoor reamer but, looking at the print on Bullets.com, I see they show the datum is .400 there. Wondering why this discrepancy?
     
  7. rardoin

    rardoin Silver $$ Contributor

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    S4F....as long as the datum you are measuring is no sitting near the body/shoulder or shoulder/neck junction the actual one you choose has no bearing on the results one is ttrying to obtain. I like the 0.400" datum as it sits more in the center of the shoulder and I use it on another cartridge also. The .375" datum would serve my purposes well but sits to close to the neck on my other cartridge I measure and I am too lazy to swap out the insert;).
     

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