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Thread: Do I trim new factory brass?

  1. #1
    Boolit Master novalty's Avatar
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    Do I trim new factory brass?

    I just received my new Winchester brass for reloading 25-35 in my Grandmother's old Winchester '94. For those that have loaded for this, do I trim the brass to a set length before loading for the first time? If so does anyone have a case length that they should be trimmed too. From a quick internet search I am finding a Case length at: 2.043.

  2. #2
    Boolit Master 6pt-sika's Avatar
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    I personally do not trim new brass until after I shot it a time or two . Some folks do I'm just not one of them for a lever gun !
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  3. #3
    Boolit Master 6pt-sika's Avatar
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    I go by whatever the loading manuals say and if it says 2.043" I would most likely trim to 2.040" .
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    Double's , 6.5mm's , 444 Marlin , Sika Deer and my family in the Philippines

  4. #4
    Boolit Master
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    It depends. If the new brass is all of the same length, and close to the listed trim-to length, then it's probably fine and dandy. You'd have to measure enough cases to see if they're consistent.

    You need a consistent case length to get a consistent crimp.

    If you're crimping into a crimp groove, then of course a consistent case length will mean consistent placement of the groove relative to the case mouth during bullet seating. If you set your seating die to place the front drive band almost touching the case mouth, and you insert a longer case, you're now jamming the case mouth into the bullet's drive band. Stuff like that.

    I have some new Winchester cases, some of which need to be trimmed, and some of which are too short to get a proper crimp. I also have some Starline brass that is very consistent, so I don't have to mess with it.

    It can get more complicated than that, depending on your chamber dimensions and the bullet you're using, but those are the issues I'm dealing with on the 30-30 and the 10mm Auto. If my cases are consistent within a few thou, their exact length is not so important in my situations, but in others, the exact length may be an issue.

  5. #5
    Boolit Master

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    +1 on omnivore

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  6. #6
    Boolit Master shredder's Avatar
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    All the new brass I have ever used came with out of round case mouths and very rough edges. I can not imagine how anyone could seat a boolit without a trip through the resizing die(backed out 1/2 turn), trim and chamfer/deburr. Then you are starting with all your cases exactly the same. Just my 2 pennies.

  7. #7
    Boolit Master
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    New brass needs to be sized then measured for length, trimmed if needed according to what Ominvore posted above.
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  8. #8
    Boolit Master novalty's Avatar
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    Thanks for the advice. I'll put it through my sizer die first and measure and proceed from there.

  9. #9
    Boolit Master
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    I FL size, run them through the trimmer and then chamfer. It takes me just as long to measure them as it does to trim. If they're short than they aren't trimmed so no big deal. I only do this for bolts/levers. For straight wall pistol I just size and load as normal.


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  10. #10
    Boolit Master pietro's Avatar
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    Quote Originally Posted by shredder View Post
    all the new brass i have ever used came with out of round case mouths and very rough edges. I can not imagine how anyone could seat a boolit without a trip through the resizing die(backed out 1/2 turn), trim and chamfer/deburr. Then you are starting with all your cases exactly the same. Just my 2 pennies.

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  11. #11
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    I like to fit my cases to the chamber of the rifle it will be fired in. Especially for use with cast bullets which do not like to jump the gap. Double especially, you should check the needs of your rifle if it is an old rifle. Some of the older rifles are found where the chamber lengths where not held to modern standards, in other words, "loading book trim to lengths". (I mostly shoot 100+ year old rifles rifles)

    As a mater of practice I have found even current production rifles have correct length-plus chambers running 0.025 to 0.035" too long. By trimming to stated length you end up with short cases. Your rifle does not know or care what the book said. When handloading and especially for cast bullets, we can accommodate this to our advantage to produce more accurate, less leading ammunition.

    I won't go into how the correct length is determent. Plenty has been written elsewhere about that. You should trim to what ever the "book" says if that is beyond your handloading at this point in time.

    There are many benefits to having the correct, full, safe length cases when shooting cast bullets.
    Last edited by Chill Wills; 09-21-2012 at 12:06 AM.
    Chill Wills

  12. #12
    Boolit Master
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    novalty wrote: Thanks for the advice. I'll put it through my sizer die first and measure and proceed from there.
    Excellent idea running all the brass thru a resizer first. Then you can trim them anywhere between 2.020 and 2.040 just so long as they all are the same length after trimming is what your looking for.

  13. #13
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    +1 to all the previous posters who mentioned fitting the brass to the chamber. How will you know what your trim-to length is without knowing the length of your chamber, especially on a very old gun? A chamber/throat cast or impact slug is in order.

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  14. #14
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    rintinglen's Avatar
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    Heck yeah. Brass varies in length way too much not to trim it. A while back I measured 100 38 Special cases from Starline. None of them was long enough to exceed the trim to length and what I had measured ftom 1.133 to 1.146. If your brass starts out all over the map, your shots on target will reflect that.
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  15. #15
    Boolit Master


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    Most certainly! At this point I'd want to establish a baseline. First, measure each case to ensure none were over max. I'd fire each case with a starting load then resize and trim to SAAMI minimum length. WW and RP factory cases have been a bit troublesome for me lately; awesome brass but lengths vary. I'm fussy about case lengths on cases that require a crimp.
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  16. #16
    Boolit Mold
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    I shoot 45c out of a rbh,bought some starline brass,over half were shorter than the trim to length in the manuals.Can I just trim to the shorter length and load?

  17. #17
    Boolit Man
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    Quote Originally Posted by northernlead View Post
    I shoot 45c out of a rbh,bought some starline brass,over half were shorter than the trim to length in the manuals.Can I just trim to the shorter length and load?
    How short are we talking?

  18. #18
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    I always FL size and trim. Even the ready to go brass isn't ready to go IMHO. Right or wrong, that's how I was taught by my father and have always done it that way.
    Last edited by osteodoc08; 08-28-2017 at 06:19 PM.

  19. #19
    Boolit Master
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    Just bottle neck rifle brass. Size first then trim. My .270 was bad about having to trim every other loading. My straight wall pistol and revolver cases never again. I did that once to my .44 brass while recuperating from surgery. Yes, I was bored. Never again....
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  20. #20
    Boolit Master gnostic's Avatar
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    I give new rifle brass the whole treatment, trim after sizing, case mouth bevel, flash hole and primer pocket.

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