need to trim new brass???

Discussion in 'Reloading' started by dmax1800, Jun 14, 2013.

  1. dmax1800

    dmax1800 Well-Known Member

    Messages:
    170
    Joined:
    May 8, 2013
    I am new to reloading. I've read that you need to measure everything and be absolutely consistent. I just got 100 Norma brass in 300 win mag. Just out of curiosity I measured the length of 10 randomly selected cases. They range from 2.06065 to 2.6120 inches in length. Is .0055 too much variance in new brass? Should I trim the new cases to get them exactly the same length before firing them for the first time? Will the variance in length effect accuracy is my biggest question. I know that you should trim the cases during the reloading process after they have been fired. I have the inserts to measure the chamber length.

    Thanks.
     
    Last edited: Jun 14, 2013
  2. Kevin Thomas

    Kevin Thomas Well-Known Member

    Messages:
    1,256
    Joined:
    Feb 16, 2009
    dmax,

    Trimming is a safety measure, and is required to ensure the case mouths don't encroach on the throat too much. The cases will tend to stretch a bit as they go through the firing/reloading cycles. Some calibers are worse about this than others, the intensity of the load as well as the way in which it was resized, and a host of other factors come into this as well. But new brass, right out of the box, should never need to be trimmed or sized. The variation you're seeing there won't be a problem at all.

    We (Lapua) do recommend running new brass over an expander mandrel before the first loading, just to uniform neck tension and round out case mouths that may have been dinged or knocked out of round during shipment. Not really a reloading step per se, but just a little due diligence to make sure everything's "right" on that first go-round.
     

  3. Beluebow

    Beluebow Well-Known Member

    Messages:
    107
    Joined:
    Dec 6, 2004
    Load, shoot then trim.I try to not remove any more brass that it takes.Use the short ones as sighters or foulers,,,they will get longer.:)
     
  4. varmintH8R

    varmintH8R Well-Known Member

    Messages:
    1,123
    Joined:
    Dec 12, 2011
    I generally trim new brass to trim-to length for two reasons:

    1. I get an equal index point to deburr the flash holes.

    2. I can measure my work-up loads to see if any combinations exhibit relatively high or low stretch after firing.

    Normally I don't resort to name calling, but if you follow my advice regarding brass over Kevin's you are dumb. :D
     
  5. Bullet bumper

    Bullet bumper Well-Known Member

    Messages:
    1,042
    Joined:
    May 20, 2009
    You might be from Lapua but I disagree with one thing . New brass is not always square at the mouth and triming to square it up is a good idea as a square case mouth helps accuracy . Also squaring up the mouth and correct chamfering helps neck sizing and bullet seating .
    Also some minimum spec chambers will actually need some factory brass to be sized down slightly just to get them in . Never say never .
     
  6. MontanaRifleman

    MontanaRifleman Well-Known Member

    Messages:
    6,068
    Joined:
    May 21, 2008
    I have never found any significant accuracy issue with necks that are not exactly the same length. New brass is usually shorter than spec and some more than others. My practice is not to trim to length until after the first firing and sizing.

    You have about 6 thou of variance. Take your calipers and open them to 6 thou to see what it is.
     
  7. Gene

    Gene Well-Known Member

    Messages:
    1,326
    Joined:
    Jan 23, 2007
    Trim about 005" - 010" below SAMMI length. Check again after first firing. Don't forget to champfer case mouths.
     
  8. Mikecr

    Mikecr Well-Known Member

    Messages:
    4,269
    Joined:
    Aug 10, 2003
    I agree with Kevin and Mark. I trim after fireforming and re-chamfer.
    My trim length is 5-10thou under chamber end(not SAAMI), but if you're running a cartridge that's expected to grow with reloading cycles, and you don't have a gracey on the bench, you can trim more off.
     
  9. 25.06

    25.06 Member

    Messages:
    16
    Joined:
    Jan 15, 2010
    DMAX1800,
    You may want to check the Math on the difference on the brass measurements.
    Have a great day.
     
  10. varmintH8R

    varmintH8R Well-Known Member

    Messages:
    1,123
    Joined:
    Dec 12, 2011
    Looks like there is an accidental "0" in there. Otherwise he has a bigger problem than trimming. But, being able to measure to hundred-thousandths would be cool.
     
  11. Bullet bumper

    Bullet bumper Well-Known Member

    Messages:
    1,042
    Joined:
    May 20, 2009
    I agree neck length is not as important as neck squareness . However it's one of those minor case prep jobs that is hard to prove that it helps all by its self .
    I find it helps bullets seat straight and bushings size straighter .
    Start with a square well chamfered neck is basic in my system .
    Most factory chambers are around .015 to .020 longer in the neck area than factory brass anyway .
    I don't trim to an actual length it's irrelevant to headspace , seating depth or OAL . I trim to slightly shorter than the length of the shortest case in a batch so they all come out square and the SAME length . When you seat a bullet you set the OAL or seating depth whichever you are working with , either magazine length or ogive distance from the lands .
     
  12. MontanaRifleman

    MontanaRifleman Well-Known Member

    Messages:
    6,068
    Joined:
    May 21, 2008
    Some valid points for trimming before firing. I figure shooting unfired brass typically gives slightly different results anyway, especially if you neck size only (I don't) and I have not seen significant differences in results by not trimming until after the first firing. I like my necks to be as long as possible for a few reasons and I figure waiting until after the first firing accommodates that, especially with sharper shouldered cases that don't much if at all.
     
  13. longrangehunterII

    longrangehunterII Well-Known Member

    Messages:
    449
    Joined:
    Jan 3, 2013
    Here's something to consider? Someone or some machine cut the chamber, and not every chamber is cut to an exact perfect measurement each and every time! The person doing the reamer work might not have held to the measurement stated by the published (SAAMI) maximum chamber length! lightbulb

    I always measure the chamber before resorting to trimming to the published trim lengths by using a Sinclair Chamber Length Gage. It's a simple item that is seated into a fired case that the neck is cut way back and chambered. I have found rarely are they cut to the published trim lengths! Most notable what I have found is that they are cut longer then the published maximum trim lengths, onetime grossly too long that timing would have never become necessary! This instance was a barrel chamber cut by Shilen Rifles while using a body reamer and a different piloted neck reamer that opened up to the proper neck to size of the case. Had I not measured the case length I would have been trimming way beyond the actual chamber length and in this case a charred area would have developed between the point where the case mouth stopped (trimmed neck), and the where the chamber actually ended! I actually sent back that barrel because of that mistake made, and unfortunately my 25" barrel is now 24 1/2" inches but the chamber was cut closer to maximum but still very long!

    When I mean too long, the chamber actually measured 2.1585" inches long, which is 0.0585" longer then the published length of a case, and 0.0685" longer then the trim to length. After is was cut a second time, it measured 2.1445" when it should have been cut to something like 2.11-2.1150" which is what the reamer Company had them set up for, but the person doing the cutting needs to pay attention to the depth of the cut for that measurement to be produced.

    For an actual measurement to find your individual rifle(s) chamber length to trim to, I'd invest in the six bucks for the Sinclair Chamber Length Gage. It's cheap and very easy to use, otherwise you just might not be trimming your case necks to the proper length? Which could be longer or shorter the the published trim length your cutting them to? lightbulb

    Why over trim a case when you have no idea how long the chamber actually is. On another note, it would be worse to have the chamber cut too short which is why they tend to be cut so long.
     
  14. Mikecr

    Mikecr Well-Known Member

    Messages:
    4,269
    Joined:
    Aug 10, 2003
    It's always stunned me to hear a reloader concerned with numbers in a book, while holding the actual items in-hand to simply measure..
    How blind does it get?