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Chambering Changing OAL

Discussion in 'Handloading and Reloading' started by peeplwtchr, Oct 17, 2020.

  1. peeplwtchr

    peeplwtchr Member

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    Hi All-

    I was testing some Titegroup in 9mm today, and saw that when I chambered them in my PCC, they OAL went from 1.102 to 1.105. I'm pretty sure that won't change performance, but just curious why that happend. 1.02 OAL, .378-9 crimp.

    Maybe my Lee sizing die?

    Thanks
     
  2. LiveLife

    LiveLife Member

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    Momentum of chambering moving the bullet forward while the extractor holds the case rim?

    Are all the rounds going longer?

    BTW, I use maximum .378" taper crimp for .3555"-.356" diameter bullets (.377" for .355" sized bullets).
     
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  3. Walkalong

    Walkalong Moderator Staff Member

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    Which is it? 1.020 or 1.102

    If they went from 1.102 to 1.105, I don't see an issue.

    If they went from 1.105 to 1.020, you have a problem.
     
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  4. peeplwtchr

    peeplwtchr Member

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    Sorry, it's 1.102 to 1.105.
     
  5. peeplwtchr

    peeplwtchr Member

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  6. LiveLife

    LiveLife Member

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    Then looks like it's the chambering action that's making the bullets move forward in case.

    As Walkalong posted, I don't think it will be much of an issue as if all the rounds are being chambered to 1.105" and "plunks" at 1.105", then your "chambered OAL" is all 1.105". ;)
     
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  7. peeplwtchr

    peeplwtchr Member

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    And 1.105 is the point where the .356 bullet meets the Lands, which is why it stops growing in length right?
     
  8. LiveLife

    LiveLife Member

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    Dang, really?

    So if 1.103" your max OAL?

    Mind if I ask what PCC/barrel and bullet you are using?
     
  9. peeplwtchr

    peeplwtchr Member

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    Yeah, I just started reloading (9mm), not doing rifle until I get all the theory; following recipe. So yes to the bullet meeting the lands?

    The PCC is an Extar EP9. The BCG is really heavy, and slams into battery with more force than an AR.
     
  10. LiveLife

    LiveLife Member

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    Are you loading to 1.103" just because published load data listed 1.100"?

    Or is that the max OAL that will allow the round to freely drop in the barrel and spin without hitting the rifling?

    Blowback action PCC requires heavier combined BCG/buffer weight (19-22 oz) to hold case longer in the chamber before moving back from recoil - https://www.thehighroad.org/index.p...es-and-what-parts-did-you-use-and-why.825314/

    I use around 20 oz combined weight for my Just Right/PSA/New Frontier PCC builds but some 3-gunners even go up to 23+ oz using stiffer .308 buffer spring instead of .223/5.56 buffer spring.

    And according to Extar website, looks like they could be using stiffer recoil spring rate also, which would slam the BCG harder. You have any issues with last round bolt hold open (LRBHO)?
     
    Last edited: Oct 17, 2020
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  11. peeplwtchr

    peeplwtchr Member

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    No, my target was 1.100, this round came out at 1.103.

    The recoil spring does appear to be very stiff. No issues on LRBHO.

    Good info. as usual, thanks!
     
  12. higgite

    higgite Member

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    Are you familiar with the plunk test to determine the max OAL for that bullet in that gun? If so, great. If not, google it. Either way, plunk test that bullet in that gun and report back. Only then can we answer your question.
     
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  13. edwardware

    edwardware Member

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    If you measure closely enough, semi-auto chambering almost always changes COAL. If you don't believe me, grab a box of factory premium ammo and your calipers, and go measure.

    In the end, a couple thousandths doesn't make a whisker of difference. If can matter if your administrative handing results in full-speed rechambering of the same cartridge tens or hundreds of times.
     
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