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Case mouths have a lip - once fired .308, what's the cause?

Discussion in 'Handloading and Reloading' started by IMtheNRA, Nov 18, 2019.

  1. IMtheNRA

    IMtheNRA Member

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    This is a problem with once fired brass that was not fired in my own rifle. A mix of random rifles at the range, not just one troublesome rifle. Cases are once fired, mostly Federal .308, as well as some other brands, including once fired Lapua.

    After resizing, I noticed that some cases don't want to go into my Giraud shell holder for trimming. Upon close inspection, I see these cases have formed a burr-like lip on the outside of the case mouth, which prevents them from entering the Giraud case holder all the way.

    The cases with the lips measure 0.341 at the outside case mouth, while the trimmed cases that already entered the Giraud case holder and got trimmed, come out with the outside case mouth measurement of 0.335

    This excessive lip is observed only on once fired brass that I picked up and full length resized in the RCBS small base die which is equipped with a Lyman carbide expander ball. Sometimes I get about 50 per cent rate with the lip, sometimes zero per cent.

    Once I use the cases in my own rifle, and resize them again, this lip is never formed again, or at least is not formed to the extent that i can't insert the case into the Giraud case holder.

    From what I can tell, the only way to remove this lip is to use the Lyman deburring tool to shave it off.

    I'm wondering if this lip is formed in my resizing die, in other people's rifle chambers, or is it just what once fired brass is supposed to be like due to some effect of factory ammo manufacturing.

    My goal is to avoid the lip so that I can easily and conveniently use my Giraud case trimmer on once fired brass that I can pick up at my gun club.
     
  2. FLIGHT762

    FLIGHT762 Member

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    Start with taking some of the suspected once fired brass that has the lip on them. Take a jeweler's loupe and inspect the lipped cases under magnification.

    Take some of the once fired cases and inspect them to see if the lip is on them prior to resizing. F/L resize some cases that do not have the lip and then check to see if any have formed a lip after resizing.

    You need to determine if the cases have the lip on them prior to resizing or your sizing die is creating the lip. Maybe you have a burr on something in your die. Should be easy to figure out where the lip is coming from.
     
    Slamfire likes this.
  3. Blue68f100

    Blue68f100 Member

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    Are you using a body die that doesn't not touch the necks?

    Do what flight762 says and locate where the lip is coming from.
     
  4. MtnCreek

    MtnCreek Member

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    Is this an X die? The RCBS die that once trimmed to a certain length, you don't have to trim again?
     
  5. IMtheNRA

    IMtheNRA Member

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    Not an X die, nor a body die. Just a plain RCBS small base full length die. I'll follow Flight's suggestion and dig up some once fired brass to measure and check under the the 40x microscope on my reloading bench. Will post results and photos here tomorrow.
     
  6. Bfh_auto

    Bfh_auto Member

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    Is it what's left of the factory crimp? Some factory loads are crimped excessively. I've seen this in Federal 22-250 brass.
     
  7. 243winxb

    243winxb Member

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    Sizing some brands of brass from 308 to 243 in a bushing fl die, with no bushing, produced a case mouth flare for me. .

    The brass has taken a set & is trying to return to its orginial form. My guess.

    Your range brass may have been fired in a rifle with excessive chamber neck diameter. I would measure the fired diameter of the necks, before sizing.

    Sizing the neck diameter down too much in one pass seems to be the problem?

    This flare has been online before, using bushing dies, with bushing, if thats what your seeing with your standard fl die.? It is a strange occurrence.

    Note: I do not recommend sizing down 308 to 243. Just buy some new 243 Win. brass. I was testing/measureing the hole in the 243 bushing die.
     
    Last edited: Nov 20, 2019
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