Case length question.

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  • #16
    I think some of you are mixing issues here so let me see if I can help clarify; case length is independent of head space. A go or no-go gauge is measuring head space which is the distance between the bolt face and a datum line on the shoulder of the case. It doesn't care about the neck length. It is possible to set head space correctly yet encounter a dangerous situation if the case neck is long enough that it is forced into the throat. This will cause the case mouth to be crimped into the bullet. This in turn will cause much higher pressures before the case mouth releases the bullet.
    If the load is near maximum, and the case mouth is driven into the throat, then pressure will escalate rapidly until something gives. Usually this would be a blown primer and maybe a flame cut firing pin but could be worse.
    This isn't likely with most Grendel chambers because there is ample room for the case to grow before this would occur. But not all chambers are the same. I have one early Grendel Reamer that requires a neck turn and has zero lead to the throat. With this chamber you had better trim and turn cases for or you will have major issues.
    Bob

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    • Bill Alexander

      #17
      We made a mistake in our (AA) published figure for the case length. The chamber will easily absorb cases until they split but as most reloaders want a trim length I went with a figure that should not be exceeded and then a tolerance. ie once the case gets beyond 1.526 it should be trimmed back to between 1.526 -0.006. This is a reasonable tolerance for any small hand tool and a pair of cheap calipers.

      In the absence of a temperature controlled inspection facility and laboratory type CM to measure the lengths I still find some quandry in asking someone to trim a piece of brass to an exact length +/-.000x nor should it be necessary. I frequently wonder during discussions such as these how a small mass produced hand tool can acheive a repeatable tolerance that exceeds a multi thousand $ CNC machine but that is my cynical nature.

      Factory new brass is well short of the chamber transition and brass will rarely grow such that it demands to be trimmed. Hornady and Western both work from the case print so if in doubt use thier figure.

      As we print updates to our load data we will correct our trim figures.

      Comment


      • #18
        Originally posted by stokesrj View Post
        I think some of you are mixing issues here so let me see if I can help clarify; case length is independent of head space. A go or no-go gauge is measuring head space which is the distance between the bolt face and a datum line on the shoulder of the case. It doesn't care about the neck length. It is possible to set head space correctly yet encounter a dangerous situation if the case neck is long enough that it is forced into the throat. This will cause the case mouth to be crimped into the bullet. This in turn will cause much higher pressures before the case mouth releases the bullet.
        If the load is near maximum, and the case mouth is driven into the throat, then pressure will escalate rapidly until something gives. Usually this would be a blown primer and maybe a flame cut firing pin but could be worse.
        This isn't likely with most Grendel chambers because there is ample room for the case to grow before this would occur. But not all chambers are the same. I have one early Grendel Reamer that requires a neck turn and has zero lead to the throat. With this chamber you had better trim and turn cases for or you will have major issues.
        Bob
        Bob,
        If my explanation is misleading I never meant it to be even though I did not explain in detail headspace vs neck length as well as you did. The point I was attempting is that another manufacturer/gunsmith could shorten or lengthen the neck length. Thus creating the bullet crimping that you and I have attempted to explain, like you put it this doesn't affect Headspacing rather defines the trim length to control the neck length. Headspace is a completely different issue as it deals with a datum Dia in the shoulder to a back of case. Because, I have the AA Chamber I would go by what AA defines. My observation sthus far is that none of my brass has made it to the recommended max length (headspace of my brass is defined by my dies, not a trim length)

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        • Greyfox
          Bloodstained
          • May 2011
          • 56

          #19
          I had a loaded round that would not chamber. I found out that the brass was over 1.526". I pulled the bullet and trimmed the brass back to 1.520,reloaded it, and it chambered just fine. None of the other cases I have were long like that one. My rifle is an Overwatch.

          Comment

          • sneaky one
            Chieftain
            • Mar 2011
            • 3077

            #20
            Just like any other manufacturers rifle chamber-no two are the same. As long as we know our own specs., we can trim-or not.

            Comment


            • #21
              Originally posted by sgt_murf View Post
              Bob,
              If my explanation is misleading I never meant it to be even though I did not explain in detail headspace vs neck length as well as you did. The point I was attempting is that another manufacturer/gunsmith could shorten or lengthen the neck length. Thus creating the bullet crimping that you and I have attempted to explain, like you put it this doesn't affect Headspacing rather defines the trim length to control the neck length. Headspace is a completely different issue as it deals with a datum Dia in the shoulder to a back of case. Because, I have the AA Chamber I would go by what AA defines. My observation sthus far is that none of my brass has made it to the recommended max length (headspace of my brass is defined by my dies, not a trim length)
              I understood your post, and it is clear, I was referring to earlier posts in which some were thinking as long as the bolt would close the case length would be in spec.
              Bob

              Comment

              • BjornF16
                Chieftain
                • Jun 2011
                • 1825

                #22
                Originally Posted by Bill Alexander

                As we print updates to our load data we will correct our trim figures.
                Looking forward to Rev 3 of the AA Reloading Data...
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                • billy
                  Unwashed
                  • May 2015
                  • 11

                  #23
                  I realize this is an ancient thread, but I have stumbled across something interesting. I purchased 200 rounds of 123gr scenar directly from AA, and a box of 123gr A-max from a local gun shop. The AA ammo uses Hornady brass (as does the A-max of course). After once-firing on both (did not measure before), the AA is between 1.526-1.531, yet the A-max is 1.516-1.520. Is it possible this is due to higher pressure in the AA loads, or could it be that Hornady trims more on their factory fodder?

                  [UPDATE] The Lee hand trimmer is set up for 1.516. I am hoping that the .006 tolerance Bill A. mentioned is still valid for their current (4th edition) minimum of 1.520.

                  [UPDATE 2] A a minor side note, the longer AA brass makes using the Lee hand trimmer wear out your hand after about 40 rounds (for me anyway).
                  Last edited by billy; 08-06-2015, 06:30 PM.

                  Comment

                  • LRRPF52
                    Super Moderator
                    • Sep 2014
                    • 8569

                    #24
                    Grendel SAAMI chamber length to the neck mouth is 1.530". What barrel do you have, and what chamber is in it? 1.531" is pretty long for a first time firing. Can't say I've ever seen that really.
                    NRA Basic, Pistol, Rifle, Shotgun, RSO

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                    6.5 Grendel Reloading Handbooks & chamber brushes can be found here:

                    www.AR15buildbox.com

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                    • billy
                      Unwashed
                      • May 2015
                      • 11

                      #25
                      AA, 24" Overwatch upper. I just found one that was 1.536.

                      Comment

                      • Old Soldat
                        Bloodstained
                        • Dec 2015
                        • 36

                        #26
                        Recently received 100 pcs of brass from A/Arms, not 1 pc was over 1.520"-all shorter. Go figure.

                        Comment

                        • Sputnik
                          Warrior
                          • May 2013
                          • 503

                          #27
                          And to add to the confusion, Hornady reloader manual version 8 has max case length of 1.516 with a trim length of 1.506. Their version 10 states max case length of 1.520 with a trim length of 1.510. What changed?

                          Comment

                          • Drillboss
                            Warrior
                            • Jan 2015
                            • 894

                            #28
                            This bugged me a little when I started reloading the Grendel, so here's my interpretation, with no data to back it up.

                            I suspect Alexander Arms first published their trim lengths to be few thousandths below the chamber neck length of 1.53", which should be a safe recommendation.

                            I'm guessing Hornady published their initial data after SAAMI specification, when they recommended a length a little below the SAAMI max cartridge case length of 1.52". In the tenth edition, they are showing max case length of 1.52", same as SAAMI. They also recommend a trim to length of 1.51", which is well above SAAMI minimum of 1.50".

                            How cautious do you want to be? I'd think you're fine keeping the case length a few thousands short of 1.53", thus keeping your neck length as long as is reasonable.

                            Comment

                            • diddlyv
                              Warrior
                              • Aug 2016
                              • 352

                              #29
                              The amount any given case will grow is a function of how far the shoulder is set back during resizing. Move it back a lot and a lot of brass will be pushed into the neck. Move it back just a bit and just a bit of brass will be forced into the neck. Back in my high power M1A days pretty much had to trim every time I resized my 7.62 brass. I essentially sized my cases to the length of the Die as the die always made contact with the shell holder. One certainly did not want any issues chambering rounds during a match. Cases were only good for about 5 firing before one started seeing the tell tale ring indicating a high probability of a case head separation on the next firing so the brass was pitched.

                              I have evolved somewhat over the last 20 some odd years and now use comparators. My goal on the Grendel is to only set the shoulder back about .003 - 4. Pretty sure that will keep the case from growing very much.

                              When I do trim I generally like to trim to the specified length +.002 - .000 as I don't want the necks too short and don't want to waste time trying to hold +- .000 given the generous difference between max case length and trim to length.
                              Last edited by diddlyv; 06-20-2017, 04:07 AM.
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                              • LRRPF52
                                Super Moderator
                                • Sep 2014
                                • 8569

                                #30
                                Grendel working pressure is much lower than .308, .260 Rem, or .223, so I find that I never need to trim necks for length.

                                I also like as much neck tension as I can get, and since 6.5 Grendel is less than a caliber in neck length, I avoid unnecessary trimming if I can.

                                The only brass I've seen exceed 1.530" length is PPU, which is recalled.

                                I found with the Hornady comparator tool that I need to set back my shoulders .006" or I won't get bolt closure. I use the .350" bushing in the comparator set, and zero out on that once I install it on one side of the calipers.
                                NRA Basic, Pistol, Rifle, Shotgun, RSO

                                CCW, CQM, DM, Long Range Rifle Instructor

                                6.5 Grendel Reloading Handbooks & chamber brushes can be found here:

                                www.AR15buildbox.com

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