Measuring Case Length with Comparator

Discussion in 'Reloading' started by Jzeman56, Sep 20, 2018.

  1. Jzeman56

    Jzeman56 Member

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    I have approx 120 rounds of 300 win mag that I want to reload (I'm new to reloading). I was looking at what I documented last night and from the shoulder measured with a comparator, all cases average 2.2715 (.270 is shortest; .273 is longest). If I just measure the OAL case length without the comparator, I get 2.0403 as an average. Wouldn't the length from shoulder with a comparator be a shorter reading? This is all once fired brass. Case Max Length is 2.262 by SAMMI specs. If I put the cases into my lyman E-ZEE case length gauge, they all fit?

    Average for 20 cases:
    Shoulder length with comparator = 2.2715
    OAL case length = 2.0403
    Shoulder Diameter = .4914
    Web Diameter = .5134
    Neck Outside Diameter = .3419
    Case Neck Thickness = .013

    Am I doing something incorrectly? Case Measurements 300 win mag.JPG
     
  2. PowellSixO

    PowellSixO Well-Known Member

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    Take some pics of where you are measuring from, and post them. Something is definitely wrong. Lol. I don't see how it's possible for you to get a 2.0403 reading from anywhere on that case.
     
  3. bigedp51

    bigedp51 Well-Known Member

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    Your comparator measurements are fine, and you zero the calipers to make up for its added length. And you zero the vernier caliper again for OAL readings with the comparator removed.

    All you need to do is let your cases headspace on their shoulder so adjust your die for minimum shoulder bump below comparator readings.
     
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  4. PowellSixO

    PowellSixO Well-Known Member

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    You're comparator readings should be measuring somewhere between the 2.1961" and 2.3563" reading. You should be measuring the shoulder with the comparator. Which you seem to be reading correctly. The 2.0403 is what has me confused. Maybe like bigedp51 said, you're not zeroing your caliper.
     
  5. Jzeman56

    Jzeman56 Member

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    Here are some screen shots of how I'm measuring...
     

    Attached Files:

  6. Jzeman56

    Jzeman56 Member

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    I just double checked myself again.. I put the calipers together, zero them out and then measure and getting 2.04+. Bad calipers or battery perhaps?

    what has me confused is sammi max length is a lot shorter than what I have measured. My plan was to bump back .001 (at least at this point). If it chambers I should be good right or should they be trimmed back to sammi specs? Confused at this point on whether I should trim or not.
     
  7. PowellSixO

    PowellSixO Well-Known Member

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    Something is wrong with your calipers I believe. I understand why you were confused now. Haha.
     
  8. PowellSixO

    PowellSixO Well-Known Member

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    If your calipers were correct (which they might be on your comparator readings), I would keep adjusting the resizing die tighter and tighter, until I achieved a 2.2700" reading. Bumping the shoulder back .0015 is about perfect in my experience.

    But since they seem to be acting weird, I wouldn't do anything else until I got a new pair of calipers to redo my measurements.
     
  9. Jzeman56

    Jzeman56 Member

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    Thanks everyone... I wanted to double check my sanity! I will start by replacing the caliper battery and if still having issues, will probably purchase a new one.
     
  10. rfurman24

    rfurman24 Well-Known Member

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    Ya, your comparator measurement is right on. Obviously your OAL is not. I would replace the battery first but I would guess your caliper is bad. What does it do as you slowing increase the measurement? You could compare it to a ruler for a rough check on where it is messing up.
     
  11. tierradelmundo

    tierradelmundo Member

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    I have that exact caliper, it is very sensitive to the condition of the battery, and how hard the battery is being held in. I've folded up a very small piece of duck tape and put that between the battery and the battery cover to keep enough downward pressure to get a consistent measurement. The other key is to check, on a very regular basis, that it has maintained it's zero and is giving you a measurement that makes sense. Also, try not to move the caliper too fast, and avoid using the little micro-adjust wheel, that thing seems to be hardwired into the circuit that screws up the measurement.
     
  12. Jzeman56

    Jzeman56 Member

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    So.. I took rfurman24's advice and put it up against a ruler... and tried 3 different batteries. This is what I'm getting for a 1" measurement.
     

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  13. Jzeman56

    Jzeman56 Member

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    If anything it was a good practice run on using the calipers!
     
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  14. Jzeman56

    Jzeman56 Member

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    Thanks. I practically have to dig the battery out of it...