case trimming 101



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  • case trimming 101

    I am in the process of building a 9.3 x 62 mauser. I bought 100 new lapua cases which mike 2.435 ". My Barnes manual suggests 2.420" trim length. I purchased an RCBS trim die and find I cannot insert the cases far enough into the trim die. The case gets tight long before it is fully inserted. Forcing it further pushes the shoulder back. I am trying to load some dummy rounds to check feeding before I go further. Would some enlighten me on the rudiments of case trimming with a trim die? I have a Lyman trimmer and always have a little trouble getting consistency. I am sure this is a technique problem. Thanks in advance for any help. Joe

  • #2
    Trimming the 9.3x62


    My Lapua case measure 2.434"-2.435" also.

    All my manuals list the max case length as 2.441" and a trim length of 2.431". If you have a manual that list another dimension it is likely an error. My Barnes is number 3 and my six other manuals plus Ken Howells book Cartridges which confirms the measurements. Also, 62mm is 2.4410"

    Do not trim the new Lapua brass it is in the window.

    If the trim die pushes the shoulder back don't use it. Load these new cases with neck sizing only, don't contact the shoulder. If you are making dummy rounds just neck size and seat to the desired length with the bullet you want to use. COAL is 3.290" but most magazines will take longer. The smith should chamber it to those dimensions. Any properly chambered rifle will chamber new Lapua brass.

    The concept of the trim die is to set it up so the shell holder will contact the bottom of the die, then push a case in all the way and file off the excess. It is a pain in the butt. The rotary trimmer is best, especially if the die alters the case dimensions.

    Hey, great old caliber you have there, what is your rifle/action?
    Is there nothing so sacred on this earth that you aren't willing to kill or die for?


    • #3
      case length

      Yep, the rotary trimmers are usually the best to use... most of the time. They should be consistent though. I think some of the problem with them when trimming a lot of mouth off is that the shavings and sprues bind up and roll over causing increased resistance to turning. This in turn makes the user quit early on the stubborn ones- thus the inconsistent lengths. If you're getting a lot of binding the farther you cut then it's probably best to stop at that point with each case. Then lightly chamfer all of them inside and outside and then run them all thru the trimmer again. That should ease the final cutting and should give the desired consistent lengths. Sharp cutter heads help and trimming often enough so no more than a few thousandths is trimmed each time also helps. Also, a good thing to do with a new rifle is to get an exact chamber length. Unforturnately, the simplest, cheapest and easiest to use chamber length gauges don't show a gauge plug for the 9.3. Whoever reams the chamber should be able to help there or a chamber casting can be taken. If the exact chamber length is known then all the quess work is taken out. And, you can then trim correctly, maybe .010" under your rifle's chamber length. Just check the case lengths often as over-length cases can cause dangerous pressures.


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