Brass: How short is to short?

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  • Jakal
    Warrior
    • May 2014
    • 376

    Brass: How short is to short?

    Was trimming up some brass and noticed that some of the cases (33 pieces) are .002 to .010 shorter than the Minimum length as suggested by Alexander Arms.

    See Grendel Reloading Handbook Vol.1 page 38

    Max 1.526
    Min 1.520

    I have heard that trimming back .010 shorter than Minimum will not hurt and to expect the case to grow every shot since the shoulder is at a angle of 30 degrees or less.

    Factory 123grn SST case length is ~1.515 inches. Not sure why the Hornady loads are short from the start. My sized and loaded Lapua brass is about the same size as the Hornady. New Lapua (non-sized) is 1.513 to 1.516.

    Just wondering what the Hordes thoughts are on this.
    Last edited by Jakal; 10-04-2016, 06:43 PM.
    ""Come taste my Shillelagh you goat-eatin bastard!""
  • Rickc
    Warrior
    • Aug 2016
    • 311

    #2
    Originally posted by Jakal View Post
    Was trimming up some brass and noticed that some of the cases (33 pieces) are .002 to .010 shorter than the Minimum length as suggested by Alexander Arms.

    See Grendel Reloading Handbook Vol.1 page 38

    Max 1.526
    Min 1.520

    I have heard that trimming back .010 shorter than Minimum will not hurt and to expect the case to grow every shot since the shoulder is at a angle of 30 degrees or less.

    Factory 123grn SST case length is ~1.515 inches. Not sure why the Hornady loads are short from the start. My sized and loaded Lapua brass is about the same size as the Hornady. New Lapua (non-sized) is 1.513 to 1.516.

    Just wondering what the Hordes thoughts are on this.
    Actually the Hornady reloading manual says 1.510 is trim to length and 1.520 is max. My lapua brass new in box is 1.515 give or take a .001. I don't trim till I have to. like my brass kind of long. but I do trim a batch at a time. Don't want a bunch of brass of different lengths.
    Last edited by Rickc; 10-04-2016, 08:32 PM.

    Comment

    • sneaky one
      Chieftain
      • Mar 2011
      • 3077

      #3
      Guys- ? I cut mine all down to 1.515 in 2008,,,, only checked a few of Lap- AA brass. Since then= All is well. Hornady, and all the AK brass needs to be checked on your spot.
      Last edited by sneaky one; 10-05-2016, 01:16 AM.

      Comment

      • sneaky one
        Chieftain
        • Mar 2011
        • 3077

        #4
        May need to be shorter , ?

        Comment

        • Jakal
          Warrior
          • May 2014
          • 376

          #5
          So I wonder why the difference between the AA and the Hornady trim numbers.

          I'm thinking the AA barrel had a bit longer chamber and that might allow for the growth of the brass to 1.526. My 2 Lilja barrels seem to be a little tighter, brass comes out at 1.519 after being fired. My Bartlein barrel from PF, brass comes out at about 1.524.

          Looks like I'll need to trim my Lilja/Hornady brass to one size and my Bartlein/Lapua brass to another size.
          ""Come taste my Shillelagh you goat-eatin bastard!""

          Comment

          • Klem
            Chieftain
            • Aug 2013
            • 3509

            #6
            Trimming cases shorter than SAAMI is no big deal, unless you get ridiculously short.

            The Grendel case headspaces off the datum-line of the shoulder (the middle of the shoulder) so no need to be concerned about this. An example of when you do need to be careful of case length and headspace is in an auto handgun which headspaces off the case mouth.

            Two issues you might want to consider;

            Surface Area
            There is a rule of thumb where the length of the bullet shank in contact with the inside mouth of the case should be at least the diameter of the calibre. This means for the Grendel you should seat your bullets so at least 6.5mm of the shank is seated inside neck. The Grendel has about 6mm of case neck to grip the bullet. Because bullets have to be seated deep to fit in a magazine this means typically the full 6mm of the shank will be in contact (already less than the 'Rule'). The calibre rule is only a simple guide meaning you can seat less than the calibre as long as you sort out neck tension.

            Failure to Obturate.
            Trimming the case too short erodes the cases ability to properly seal. The forward half of cases are designed to expand and seal the chamber. If there is no seal the expanding gases take the path of least resistance and head back out the chamber and into the receiver. Smoke billows out of the ejection port and the powder burns slower than normal because it is not contained. The bullet will be lodged half way down the barrel. This can also happen with slow burning powder like subsonic ammunition. It's impressive to witness but not dangerous. You will need to tap out the bullet before loading and firing the next one. I've only seen this with subsonic ammo but trimming the neck until it is unable to properly seal will result in the same.
            Last edited by Klem; 10-05-2016, 04:39 PM.

            Comment

            • Cockednlocked
              Bloodstained
              • Jun 2016
              • 50

              #7
              Originally posted by Klem View Post
              Trimming cases shorter than SAAMI is no big deal, unless you get ridiculously short.

              The Grendel case headspaces off the datum-line of the shoulder (the middle of the shoulder) so no need to be concerned about this. An example of when you do need to be careful of case length and headspace is in an auto handgun which headspaces off the case mouth.
              How about the circumstance of not trimming the rifle case to at least its listed maximum length, where the neck is long enough to extend beyond the second shoulder, which would prevent the first shoulder from contacting the chamber taper, making headspace too long? Essentially, this would cause the rifle case mouth to "headspace" against the second shoulder, at the freebore. Closure of the bolt with lockup could still occur, forcing a crimp of the neck to the bullet.

              I only size my cases to the maximum length (1.516") rather than the "trim length" (1.506"); I see no need to go shorter, removing material that could otherwise help extend case life. I suppose one could measure the exact length of their chamber's neck area, to determine how much it differs from SAAMI spec, and trim their cases accordingly. I've had no issues with crimping of the case mouth or difficult extraction. Could it be that my chamber is a tad longer than spec?
              Last edited by Cockednlocked; 10-22-2016, 01:52 AM.

              Comment

              • Drillboss
                Warrior
                • Jan 2015
                • 894

                #8
                SAAMI specifies a maximum case length of 1.52" with a tolerance of -0.02" (or 1.50" minimum). The chamber begins to taper down from the 0.30" neck diameter at 1.53". Hence, even AA's recommended max length of 1.526" should still be short of the neck taper.

                I wonder if AA's numbers were established before SAAMI got involved, while Hornady's numbers are based on the SAAMI max cartridge.

                Comment

                • JASmith
                  Chieftain
                  • Sep 2014
                  • 1620

                  #9
                  Keeping the length away from the 1.53" SAAMI minimum chamber length is a very good practice.

                  One gets serious spikes in pressure when the case mouth gets in contact with the start of the compound throat, or freebore in other chambers.

                  The cause is the neck not having space to expand and allow the bullet to move as expected.
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