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Understanding case dimensions

Discussion in 'Handloading and Reloading' started by NorthBorder, Oct 4, 2012.

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  1. NorthBorder

    NorthBorder Member

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    I'm getting started in reloading and just bought a Lee Classic turret press and a set of 9mm dies. Other than that all I have is a caliper. So, the only thing I can practice now is using the resizer/decapper die. And herein lies the conundrum.

    First, I bought a Pittsburg 6" digital caliper from Harbor Freight for $20. I don't know if that is a problem in itself. It seems to be fairly consistent.

    Next, looking in my Lyman and Nosler books they both give the same case dimensions: OAL of the case is .754" and dia of the case is .380". Prior to putting a case thru the resizing/ decapping die I measure the OAL of once fired brass at .743" and the mouth diameter at .377". After resizing the OAL is .743" and the mouth diameter is .372". The case diameter at the base remains at .387". The caliper seems to vary the dimensions by .001 or .002"

    If it is important, the brass I have is Win and nickel plated FC.

    I have many questions about reloading and setting the dies, etc. But for this thread, are the measurements I am getting within normal limits? Any and all answers will be greatly appreciated.

    Terry
     
  2. KansasSasquatch

    KansasSasquatch Member

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    Your measurements look fine to me. The 9mm case isn't exactly straight walled, it is slightly tapered. The case mouth will be slightly smaller than the base until you put it through the expander die. In my experience Winchester brass tends to be a little under "trim-to" length.
     
  3. 918v

    918v Member

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    My sized FC cases come out .750"+. You should screw the die in more.
     
  4. 243winxb

    243winxb Member

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    Last edited: Oct 5, 2012
  5. 918v

    918v Member

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    .743" is too short.

    Factory unfired cases measure .748"+

    This means you are not running your brass deep enough into the die.

    BTW, 9mm chambers are .762"+ deep. Plus, when you expand the case mouth and seat the bullet, the case will get shorter still. So then you'll be running .020" of headspace. I like to stay inside of .010".
     
  6. rcmodel

    rcmodel Member in memoriam

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    I agree your sizing die isn't adjusted properly yet.

    Try this:
    1. Run the ram up all the way.
    2. Take a sheet of paper and lay it on top of the shell holder.
    3. Screw the die down until it is firmly in contact with the paper & shell holder.
    4. Lock the lock-ring.

    That adjustment insures full resizing, without any risk of the carbide insert hitting the shell holder too hard and cracking it.

    rc
     
  7. 918v

    918v Member

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    Sometimes a 9mm sizer die is not capable of sizing the case properly. In my case, the Redding die was pretty good, but I made it better by removing .030" off the top of the shell holder. This allowed the case to go in deeper and to get sized more. This resulted in an additional .003" or more case length, but more importantly it allowed the die to swage away every part of the bulge caused by firing. My fired sized brass is longer than factory unfired brass.

    If your sizer die is made in such a way that the carbide sizer ring is recessed from the bottom of the die, take material off the bottom of the die until it is flush. My Redding die has the carbide flush with the bottom.

    Some people will tell you that your carbide ring will pop out or crack if you do this, but this is not true. My die is 20 years old and has sized tens of thousands of 9mm cases. The carbide never popped out or cracked and in fact indented the top of the shell holder due to having cammed over it so many times.

    The problem with 9mm is that SAAMI spec and reality are worlds apart. You need to make the tool work for you, not the other way around. Size your brass correctly if you want to avoid reliability problems.
     
  8. NorthBorder

    NorthBorder Member

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    Ok, error on my part, I didn't read my notes correctly. After resizing, the OAL is .748". So is my die inserted to the correct depth? Also, nobody has any issues with the caliper I am using? Thanks for all your replies, they really do help me to understand.
    Terry
     
  9. rcmodel

    rcmodel Member in memoriam

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    Your caliper is fine.

    Thats the same one I use.

    It is 100% accurate & repeatable once you learn how to close it with the same amount of force as you used when you zeroed it.

    Same with any caliper or micrometer regardless of who made it, the technique of using it is 99% of the accuracy.

    Not unless you adjusted it like I said in post #6.

    rc
     
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