Measuring Chamber?

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  • Measuring Chamber?

    So, here the problem, I made a cartridge length measuring device to measure how deep the throat is cut in my chamber but I'm getting different measurements with different bullets.
    I'm using Hornady's Lock-N-Load Comparator to measure to the ogive, not overall length. Shouldn't the dimension from the bolt face to where the ogive of the bullet contacts the lands be the same for all bullets? What am I doing wrong?

    1.734 w/Sierra 120 Pro-Hunter, C.O.L. 2.217
    1.673 w/Hornady 95 V-Max, C.O.L. 2.199
    .061 difference

    This is the cartridge length measuring device I made and used:
    Hi guy's, Very new to the forum, just now starting to build a 6.5 with a Mega lowwer,a Liberty barrel from Satern and a Dillon upper,could I get some advice on the jump to start out with using Barnes TTSX ? Allso I have heard Pro's and Con's on crimping in the AR platform may I have some comments? Thank's fopr your reply Razor
    Last edited by Guest; 01-06-2012, 03:20 PM.

  • #2
    I'm not an expert but from my point of view I think all bullet with different grain i.e 95 v-max, 123 a-max. are not the same profile. even the lapua 123 scenar and hornady 123 amax have different bullet profile that's why they have variations in measurements & seating depth specially if you use ogive dimensions. I hope some will explain this much more

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    • txgunner00
      Chieftain
      • Mar 2011
      • 2070

      #3
      You will most probably get different measurements with different bullets even of the same weight because their ogive profiles vary. A comparator does not touch the bullet at the same place the lands do. Close but not exactly.
      NRA life, GOA life, SAF, and TSRA

      "I ask, Sir, what is the militia? It is the whole people, except for a few public officials. To disarm the people is the best and most effectual way to enslave them."

      George Mason, co-author, 2nd Amendment.

      Comment


      • #4
        I completely agree with 65man,

        Another way to easily measure your chamber is to close the bolt and put a cleaning rod down the hole with a flat jag on the end. Mark the rod at the muzzle. Then, take a bullet you plan to use and slide it into the chamber. Use a dowel rod, pencil or whatever to push the bullet up against the lands. Very slowly and lightly close the bolt against the stick/dowel/pencil (whatever) to hold the bullet in place. Take your calipers and measure from the muzzle to the mark you put on the cleaning rod (I like to use electrical tape to mark the rod). What you end up with is the max length you can load a round for that particular chamber using that particular bullet. You'll have to do this each time you change bullets. But, keep and log and you'll only have to do it once.

        So, after this, you've figured out the measurement for a "jammed" bullet. From here if you want to change the amount of "jump", you can just measure your cartridges and set your loading die for the desired length. Hope that helps someone.

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        • #5
          I'm just surprised at the .061 difference between bullets. I expected a little difference because of bullet profile but not that much. The more I learn the less I know.

          Comment

          • rasp65
            Warrior
            • Mar 2011
            • 660

            #6
            Originally posted by Whelenon View Post
            I'm just surprised at the .061 difference between bullets. I expected a little difference because of bullet profile but not that much. The more I learn the less I know.
            Whelenon What you have found is why it is always a good idea to measure where each new brand of bullet you use meets the rifling. You could even see some difference with different lots of bullets because as the bullet making dies wear dimensions can also change. Remember not to trust any of the OAL's you see here as all rifles are individual and need to be treated as such. Measure, measure, measure.

            Comment


            • #7
              Originally posted by rasp65 View Post
              Whelenon What you have found is why it is always a good idea to measure where each new brand of bullet you use meets the rifling. You could even see some difference with different lots of bullets because as the bullet making dies wear dimensions can also change. Remember not to trust any of the OAL's you see here as all rifles are individual and need to be treated as such. Measure, measure, measure.
              You are so right on this. At first I thought I must be doing something wrong, so I measured and remeasured, I measured 10 individual bullets of the same make and weight, then averaged. Did this with three different bullet in two barrels before it started to sink in, I'm a little slow to catch on. I might even buy Hornady's tool to hopefully get more accurate measurements.

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              • #8
                Originally posted by txgunner00 View Post
                ......A comparator does not touch the bullet at the same place the lands do. Close but not exactly.
                In the back of my mind thought on your statement is if Bill A took some scrap sections of barrel s after profiling etc etc and reamed with a AA reamer to just about the neck/Shoulder area and made it to fit the Hornady / Stoney Point device that would be about as exact as one could get. Wonder if it would be worth his time or trouble?
                Last edited by Guest; 01-17-2012, 04:46 PM.

                Comment


                • #9
                  Originally posted by Mutt View Post
                  Another way to easily measure your chamber is to close the bolt and put a cleaning rod down the hole with a flat jag on the end. Mark the rod at the muzzle. Then, take a bullet you plan to use and slide it into the chamber. Use a dowel rod, pencil or whatever to push the bullet up against the lands. Very slowly and lightly close the bolt against the stick/dowel/pencil (whatever) to hold the bullet in place. Take your calipers and measure from the muzzle to the mark you put on the cleaning rod (I like to use electrical tape to mark the rod). What you end up with is the max length you can load a round for that particular chamber using that particular bullet. You'll have to do this each time you change bullets. But, keep and log and you'll only have to do it once.
                  .
                  Especially if you set up Dummy rounds to set the dies from using Mutts suggested method. which works well, I tried this after he suggested it works good in a earlier post he had

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