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Help needed with COAL

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  • #16
    Thank-you everyone,

    just a little bit of clarification thou, i'm not looking for lands or anything like that. right i'm plenty happy just following the spec in my manual.
    the issue is more trying to figure out why i can't get the measurement twice in a row.
    i'm very much still in the learning stage. so i'm not trying to do anything fancy just measuring everything twice.
    i have loaded a couple dozen rounds and have not had any issue's so far. but i shoot the Thompson Pro-hunter platform in several different barrel's so i don't have a magazine to worry about, and i am trying to keep the loads as recommended in length -.005

    but i think i'm starting to understand all the variable's that can exist.

    i will definitely try the comparator ( just because i am curious by nature) but stick to the books recommendations.

    thank-you very much to each of you for your input.

    .

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    • #17
      If you aren't using a comparator your COAL will always vary because bullet lengths do. Grab a dozen or so bullets from the same box, measure them with your caliper, and note the variations. The seating stem doesn't use the bullet tip, it uses the ogive, see the illustration below:



      A comparator will measure off the ogive, just like the seating stem, and give consistency to your caliper measurements.

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      • #18
        Thank-you for the illustration and explanation sevenfan,
        I'm looking forward to trying that out.

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        • #19
          Once I've settle on a distance from the lands for a particular bullet, I document the measurement from the top of the seating stem to the mouth of the die. This aids in seating die set up in duplicating that oal, for that bullet, in a given rifle.

          Measuring from bullet tip to case head is unreliable and can result in varied distances to the lands, bullet tips don't contact the lands and they don't make contact with, or rather shouldn't make contact with the seating stem. If the stem is making contact with the bullet tip one needs to do something to fix that, which can be remedied quite easily..

          HBC

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          • #20
            FWIW, seating "off the lands" is the last thing in a long list of measures to improve accuracy. I always start with the bullet manufacturer's recommendation for OAL and it's the last thing I change when looking for "the load". Just fiddling with powder and neck sizing I was/am able to get 7/8" groups from my Ruger American in 308 (not every batch of bullets will vary .005"+ in length and I have some 30 cal Hornady bullets that vary just .001"-.0015"). K.I.S.S. or you can overthink reloading and spend excess time and money. Get some simple,good shooting ammo now and later when you have a better understanding of components you can try advanced reloading techniques and work with theory...
            I\'ve learned to stand on my own two knees...

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            • #21
              Totally agree with mikld.
              "The United States Marine Corps is a drug and I am a recovering addict."

              "American by birthright… U.S. MARINE by the Grace of GOD!"

              "And on the 8th day God created Marines and like fish, we came from the sea!"

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              • #22
                thank-you guys.

                i have no intentions of loading of the lands (i;m not really sure i understand what that means to begin with)
                the original question, i wanted to know if anyone can give me some advice on how to use calipers properly.
                i wanted to measure the COAL as per the manual i have..
                but every-time i measure i never get the same result twice. (almost never if i measure the same cartridge say 6 or 7 times i will get 2)
                not wanting to exceed the recommended COAL i keep seating the bullet and at some point it becomes frustrating...
                my recommended maximum is 3.200.
                not wanting to go to max i figured to be safe 3.175.
                but it seems imposible to get too...
                so i was asking if anyone can point me in the right direction..

                Thank-you everyone for all the help

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                • #23
                  Consider this Moe,

                  Pressure increases as you seat a bullet deeper, yes, BUT......

                  A .25 Auto vs. a 30'06, 10-thousandths deeper seating is one whale of a lot different.

                  10-thou removes a sizeable amount of case volume from a .25acp, 10-thou removes an amount of case volume from the '06 that is almost un-measurable.
                  Then add in fast-burning powder in the .25 and REALLY slow burning stuff in the '06, fast powders react more to seating depth differences, slow powders less.

                  Thus, A few thousandths, heck, even a hundredth or 2, makes extremely tiny difference to the firing pressure of the '06 cartridge.
                  A couple hundredths could take a .25 apart possibly.

                  The larger the cartridge, the greater the case volume, the less effect on pressure seating changes have.

                  Consider Kissing Cousins, the 10mm and the .40 S&W (10mm short).
                  Same diameter, same operating pressures, BUT, the 10mm is longer cased and uses slower powders, I've never heard of any particular KaBOOMing from the 10mm.
                  Tests have found the .40 S&W, with it's smaller initial case volume, and faster powders, if bullets get pushed back almost any at all, especially heavy bullets, pressures go right through the roof.
                  Before this was well understood .40's used to go like popcorn, LOTS of KaBOOMs.

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                  • #24
                    For practice find a standard (used to calibrate micrometers). Use it to develop your thumb "feel" and when you repeatedly get 1.000" without thinking of pressure you'll have developed the correct "feel".

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                    • #25
                      This discussion just answered my question thanks guys.

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                      • #26
                        Thank-you Guys,
                        as always great information and help..

                        Comment


                        • #27
                          Originally posted by mikld View Post
                          FWIW, seating "off the lands" is the last thing in a long list of measures to improve accuracy. I always start with the bullet manufacturer's recommendation for OAL and it's the last thing I change when looking for "the load". Just fiddling with powder and neck sizing I was/am able to get 7/8" groups from my Ruger American in 308 (not every batch of bullets will vary .005"+ in length and I have some 30 cal Hornady bullets that vary just .001"-.0015"). K.I.S.S. or you can overthink reloading and spend excess time and money. Get some simple,good shooting ammo now and later when you have a better understanding of components you can try advanced reloading techniques and work with theory...
                          When loading, seat your first load to the COAL that you want and then don't worry about the rest. Your die will seat them to where the actual point where the bullets hit the lands will be the same for the rest of your rounds. Don't measure the rest of your rounds unless you take the die out and your locking ring moves or you move the bullet seater.

                          "The United States Marine Corps is a drug and I am a recovering addict."

                          "American by birthright… U.S. MARINE by the Grace of GOD!"

                          "And on the 8th day God created Marines and like fish, we came from the sea!"

                          Comment


                          • #28
                            Accept that your never going to get all cartridges to read the same COL. I know it seems like they should, your press should be seating the bullet to the same depth every time but a sheet of paper is over .003. Very few soft point bullets are exactly the same after bouncing around in a box or a bag. I've found that polymer tip bullets are more uniform as far as COL measurement. What's more important is consistent seating depth. Rifle bullets are seated by the die somewhere between the ogive and the tip, not by the tip itself, it would get flattened if it was. If you measure bullets from the same lot you'll find they vary slightly. Be as consistent to COL as you can with what you have.

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                            • #29
                              I will change your comment a little bit. Cartridges are never to read the same COL if you measure from base of cartridge to tip of bullet.
                              I you measure from base of cartridge to bullet ogive, then they should read the same COL.
                              With the caveat that your process is consistent and you have a press and dies capable of doing it.
                              "The United States Marine Corps is a drug and I am a recovering addict."

                              "American by birthright… U.S. MARINE by the Grace of GOD!"

                              "And on the 8th day God created Marines and like fish, we came from the sea!"

                              Comment

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