Measurement to datum line

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  • Measurement to datum line

    What is the "spec" for both fired, and unfired Grendel cases when measuring to the datum line on the case shoulder using the Hornady "B" "350" gauge?

    Is this measurement any different between the Grendel, 6.5 CSS, or the 264 LBC?

    What are the measurements to the same datum line on the go, and no go gauges for Grendel/6.5 CSS/264 LBC?

  • #2
    I'm new to the 6.5 Grendel. I suspect that this relatively new cartridge has various chamber dimensions, shoulder angles, headspace dimensions, etc. Don't know this but I suspect.
    I measured factory Hornady 123 A-Max cases, fired cases from my J&T 24" HB upper, and new factory unsized Lapua cases with MY Hornady headspace gauge with the .350 insert. Multiple cases measured with repeatable various dimensions:

    ---Lapua factory new cases - 3.212" (some maybe 3.211 to 3.2115)
    ---Factory loaded Hornady 123 A-Max - 3.216-3.218"
    ---Hornady cases after being fired in my J&T upper- 3.225" average
    ---Only 2 Hornady factory cases that I've sized in my Forster Co-Ax with firm contact with the shellholder using my new Redding Full-Length die set---3.220"
    Confusing results! This is just a test of my components using my calipers and Hornady Headspace gauge with 350 insert. Looks like the Lapua cases either are sized shorter or the shoulder angle is a little different. The Hornady factory cases chambered and shot well in my upper. Your results may differ.
    Edited to add: cases measured with my new digital caliper (that I can zero with the tool attached) are in my following post.
    Last edited by Guest; 06-21-2011, 04:17 AM.

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    • #3
      I'll have to convert your measurements so I can use them. My electronic calipers allow me to reset it to zero so I get don't have to subtract off the length of the Hornady tools. Thanks for the info...I'll go do some math now.

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      • #4
        Don't know if the Hornady Headspace tool is "precision" or just a comparator. Your tool and mine may not be exactly the same. My dial calipers were at zero, then put the tool on and measured which gave the 3.2-- readings.

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        • #5
          I think the tools are measuring to a different place. Mine measures to the mid point on the cases shoulder, about half way between the start of the shoulder, and the start of the case neck. My measurements are in the 1.2 inch area.

          I think 2.260-2.265 inches is the max cartridge length that will fit into a magazine, so anything 3.2 inches long shouldn't even fit into the magazine. Even a 308/7.62 Nato cartridge has a max length of 2.810. I was starting to think centimeters, but your posting clearly has the " to indicate inches. So, I'm quite confused now.

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          • #6
            Dial caliper closed all the way, reads zero. Mounted Hornady gauge with 350 insert like in the pic. Readout reads 3.2--" with the 6.5 Grendel case inserted. My dimensions include the length of the tool plus from the midpoint of the shoulder to the case head.
            Last edited by Guest; 06-20-2011, 08:25 PM.

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            • bwaites
              Moderator
              • Mar 2011
              • 4445

              #7
              Something is NOT RIGHT....

              The total cartridge length of the Grendel should not be more that 2.27 inches, so the length to the datum line should be something like 1.2 inches.

              You need to either zero your dial after the placement of the tool, so that it reads 0.00 with the tool in place and the jaws closed, or comparisons aren't going to be exact, especially when you are talking thousandths! You are effectively measuring the length of the tool AND the datum length the way you are currently doing it.

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              • #8
                OK, for you young "electronic" generation! Forcing me to go to the store for new batteries for my piece of crap digital calipers that eats batteries. For now, all I can add is that measuring my Hornady gauge in my dial calipers the length of the tool is 2.002".
                You can subtract that from my given dimensions. Will be back when I have new batteries or a new digital caliper.

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                • bwaites
                  Moderator
                  • Mar 2011
                  • 4445

                  #9
                  Well, subtract 2.002 from 3.212, and you get 1.21, which is pretty dang close to 1.2! And that also jives with noone 1.2, or therabouts, measurements!!

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                  • #10
                    Noone caused me to go out and purchase a new digital caliper this afternoon.
                    I remeasured Factory Lapua, Factory Hornady 123 A-Max (2 different lot numbers), and my 2 cases that I've resized with a Redding Full-Length die set firmly against the shellholder of my Forster Co-Ax press( Not overly cammed over in the press but firm contact)
                    Using my new digital calipers zero'd with Hornady Headspace gauge with the .350" insert. My tool on the dial calipers measures 2.002".
                    ----Lapua factory new cases--1.207 to 1.208" mostly 1.208"
                    ----factory loaded Hornady 123 A-Max --1.216 to 1.217
                    ---factory loaded Hornady 123 A-Max fired in my 24" J&T heavy barrel--- 1.219 to 1.221
                    ----resized once fired Hornady 123 A-Max cases (only 2 just for this test)--1.215-1.216"
                    Sorry for the original confusion! Can't zero dial calipers but I should have measured the tool and deducted its length. Again, I'm surprised at how short Lapua 6.5 Grendel brass is compared to Hornady. Would be curious to know what Wolf measures. Haven't fired any of my test loads with the Lapua brass yet, but its got to grow in length some. My measurements with the dial and digital are very close but not exact.
                    Last edited by Guest; 06-21-2011, 04:35 AM.

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                    • #11
                      Sorry for causing all the trouble. We both learned something though. I learned to expect my new electronic calipers to eat up batteries...glad I have a spare one. The current battery has lasted 4 months so far.

                      I used to have a really nice standard mechanical caliper...until I took it apart to clean out some little pieces of grit in it. I never could get it back together. It went into the trash, and I found an electronic one for around $5-10. I'm still going to look for another mechanical one though.

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                      • #12
                        I was amazed to find a variety of calipers at HomeDepot. Check it out.

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                        • #13
                          sorry to dredge up an old post but after reading this post my question is. The correct Diameter to establish the Headspace measurement is it .350" or ?. I know the datum diameter must be greater than the neck and less than the Shoulder to accuraetly determin the headspace Length (?)
                          usually most cartridge this spelled out X diameter for a measurement to the base of the rim is Y for Z (GO) if Y equals something else it is in or out of specfications as designed.
                          I'm good with .350" just confirming that is the Diameter

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                          • #14
                            Originally posted by rg1 View Post
                            Noone caused me to go out and purchase a new digital caliper this afternoon.
                            I remeasured Factory Lapua, Factory Hornady 123 A-Max (2 different lot numbers), and my 2 cases that I've resized with a Redding Full-Length die set firmly against the shellholder of my Forster Co-Ax press( Not overly cammed over in the press but firm contact)
                            Using my new digital calipers zero'd with Hornady Headspace gauge with the .350" insert. My tool on the dial calipers measures 2.002".
                            ----Lapua factory new cases--1.207 to 1.208" mostly 1.208"
                            ----factory loaded Hornady 123 A-Max --1.216 to 1.217
                            ---factory loaded Hornady 123 A-Max fired in my 24" J&T heavy barrel--- 1.219 to 1.221
                            ----resized once fired Hornady 123 A-Max cases (only 2 just for this test)--1.215-1.216"
                            Sorry for the original confusion! Can't zero dial calipers but I should have measured the tool and deducted its length. Again, I'm surprised at how short Lapua 6.5 Grendel brass is compared to Hornady. Would be curious to know what Wolf measures. Haven't fired any of my test loads with the Lapua brass yet, but its got to grow in length some. My measurements with the dial and digital are very close but not exact.
                            Wolf Cases are right about 1.215 or 1.216"

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                            • #15
                              Ok am I to assume that was with a .350" Dia insert?

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