How critical is case length?

Discussion in 'Reloading Forum (All Calibers)' started by broncman, Sep 8, 2013.

  1. broncman

    broncman

    Joined:
    Nov 13, 2009
    Messages:
    1,037
    Prepping some twice fired Lapua 308 brass for upcoming match. It has all been fired with different loads and has slightly different lengths.

    Already annealed, sized, etc and at the trim stage now. For years I simply let it grow to max trim length and held it there by trimming. Since this is match loads I want to be consistent as possible.

    Sort by length and continue to let it grow till max trim length, but keep them sorted?? Or choose a length and trim all?
     
  2. watercam

    watercam Gold $$ Contributor

    Joined:
    Mar 28, 2008
    Messages:
    2,642
    For my game (NRA Long Range) I trim a batch all at once to the trim length (.010" short of max) and shoot until any one of them reach close to max. then trim all again. Usually every fourth firing when minimally sizing. Others trim (and anneal) every firing. It is all in how much time you can or want to put into it. I will say that in my sporadic bench testing (I am a coat and sling guy) I have never seen a difference in accuracy out to 600 yards with cases of mixed length. Granted we are talking about less than .003" difference over the entire box of 100.
     
  3. brian427cobra

    brian427cobra

    Joined:
    Aug 11, 2006
    Messages:
    584
    I recommend a Chmaber Length Gauge from Sinclair, chances are your brass can be 2.030 and be just fine safety wise, unless we are talking Benchrest I don't think trim lengths have much to do with accuracy, especially with 308win
     
  4. mikecr

    mikecr

    Joined:
    Nov 26, 2004
    Messages:
    3,550
    This seems like a good plan to me. Why change?
    Pick fireformed brass that's at the same lengths now for your match. When the rest catch up, add them to your match-cases.

    You trim as a result of case changes, and this means case capacity changes. Right? People match brass by weight assuming this is matching capacities. well, wouldn't they continually do this after trimming?
    If I were competing, I would have directly matched H2O capacities on the cases used for match shooting, and this would be with cases that reached desired trim length.
    My desired trim length would have been 5thou under chamber end, so that necks seal as fast as possible(reducing ES). This I'm sure would mean constant trimming in 308 form, for every sizing cycle. Which means capacity is continually changing..

    The 'improved' in wildcats counters this by improving the reloading form.
     
  5. FroggyOne2

    FroggyOne2

    Joined:
    May 14, 2006
    Messages:
    1,907
    Ken,

    I trim every time I size the brass. There is something to be said for consistency!
     
  6. hogan

    hogan

    Joined:
    Feb 9, 2007
    Messages:
    615
    Case length does not affect powder capacity, at least not that it can be "remedied/restored" by trimming. Case neck holds bullet, not powder.

    The only reason to trim is to assure that brass has not moved into neck pushing neck length beyond the chamber dimension. If neck length is longer than chamber is reamed, brass can protrude into the barrel throat and cause DANGEROUS Pressure Spike when ignited because the bullet is constricted from release by the brass in the throat...

    Sinclair used to sell a soft-steel spud that fit inside case neck and would bear against the throat-chamber to give you a reading of actual chamber neck length.

    2.005 is the industry standard trim-to length for .308win 2.010 to 2.015 is "normal" oal length for a .308win factory chamber.

    Seems to me, if you trim to 2.003 you are likely fire-etching .002 of your chamber's critical neck area with each firing. If throat is etched with each firing what about chamber area that should/could have brass protecting it?

    If your chamber neck depth is to 2.010, wouldn't trimming to that length mean your chamber integrity is being preserved by not exposing any of chamber dimension to gas & flame which an undersized trim-job would do?

    Maybe you barrel isn't getting shot-out at 3K rds, maybe loss of accuracy is result of chamber erosion caused by trimming cases too short?
     
  7. ShootDots

    ShootDots Gold $$ Contributor

    Joined:
    Jan 9, 2008
    Messages:
    5,194
    I trim my brass JUST SHORT (by 4K) of max length and once it "grows" over 2K from that point, I trim. This keeps everything more consistent than probably really needs to be>>>But once everything is "right" with a load (accuracy / tight shot strings / consistent brass prep etc..) you develop confidence in your rifle. T-Rust me, CONFIDENCE counts for a whole lot when shooting at competition! If a shot goes where it should NOT during competition, I know it was ME and not the rifle / load combination because I have confidence in my loads>>not necessarily in me!
     
  8. hogan

    hogan

    Joined:
    Feb 9, 2007
    Messages:
    615
    What really matters is chamber length oal, at least from my deductions since I began shooting switchbarrel guns in 1997. My first switchbarrel rifle was a .308win and when I got an RCBS Precision Mic, I decided the reason for its fine accuracy, even with a used factory barrel, was the minimum oal length chamber.

    The fine accuracy that rifle achieved was with (horror of horrors) Remington brass and the Sierra accuracy load for 168 bthp match bullet using IMR 4064.

    Ever since, all my bolt rifles have been switchbarrel guns and all have had chambers set to go-gauge oal, maybe go-guage plus .001 or less. Some barrels were reamed to just seat virgin brass which is under go-gauge length. Belted-magnums have been setup to headspace on the shoulder. I never trim necks below chamber dimension unless ammo will be used for hunting or defense. I use a Wilson trimmer, when I use a trimmer. I don't turn case necks.

    Point is, brass that doesn't "grow" on initial firing is better because it has encountered much less stress, and brass that is not trimmed until it exceeds chamber neck length dimension preserves chamber integrity. These are key aspects of brass which can be expected to deliver long life and precision accuracy
     
  9. broncman

    broncman

    Joined:
    Nov 13, 2009
    Messages:
    1,037
    On my last custom barrel I measured chamber length which happened to be .005" longer than max trim length. I kept all my brass to max trim length to cut down on carbon etc. This brass all came in new at 2.005". It now ranges from 2.006 to 2.012.

    Believe I will trim at 2.010 and sort the shorter ones in like groups.

    Ken
     
  10. savageshooter86

    savageshooter86 Silver $$ Contributor

    Joined:
    Sep 7, 2012
    Messages:
    2,468
    Are you FL sizing? I trim brass to 2.005 then after I shoot and FL size them they are now longer. Then trim them all back to 2.005 and load and shoot them
     
  11. finnaddict

    finnaddict

    Joined:
    Jun 2, 2013
    Messages:
    148
    Same here. Shoot, FL/BUMP, trim.
     
  12. DennisH

    DennisH Life Time NRA member

    Joined:
    May 11, 2010
    Messages:
    2,352
    All the above is good info. I agree with the above as well.

    But I normally measure about 25% of my fired brass and if I have consistant short readings, then I trim based on that reading.

    I always anneal before FL sizing.

    I really believe in brass prep. Since I started paying attention to brass prep & Bullet consistency, my groups have improved.

    Not hijacking or anything, but the bullet is as important as the brass is. I measure the bullet by bearing surface and trim meplats. Taught to me by John Hoover. It made a difference. I want <.002 runout after seating my bullet.

    Later,
    Dennis
     
  13. broncman

    broncman

    Joined:
    Nov 13, 2009
    Messages:
    1,037
    Yes I anneal, then bump/full length size every time.

    Do they make a meplat trimmer for a Wilson trimmer?
     
  14. snakepit

    snakepit Gold $$ Contributor

    Joined:
    Jan 2, 2012
    Messages:
    984
    Question, I just used my Sinclair Chamber Length Gage Insert on my Savage 6 BR and got a reading of 1.580". The Sinclair instructions have a warning that says maintain the case length so that it is a minimum of .024" shorter than the chamber length so that comes out to 1.556". Published case length is 1.560". My new Lapua brass normally shows a length 1.558". Just wanted some input on what length people thought I should be trimming to and maximum length not to exceed. I am new at reloading and not sure if I have been doing it correctly. I have been shooting to 1.560" and trimming back to 1.558"
     
  15. DennisH

    DennisH Life Time NRA member

    Joined:
    May 11, 2010
    Messages:
    2,352
    Never heard of one and just checked their website and didn't see a meplat trimmer.

    Dennis
     
  16. Raythemanroe

    Raythemanroe Bullet Whisperer Silver $$ Contributor

    Joined:
    Oct 28, 2012
    Messages:
    4,131
    I don't know how much difference it makes but I feel that having the same length case through all your rounds helps with consistent neck tension!
     
    JohnD likes this.
  17. 338 Mollett

    338 Mollett

    Joined:
    Sep 2, 2013
    Messages:
    1,016
    Hogan, very good idea on the short necks. I had Dave Tooley rework a 338 he siad the neck was beat up, I wondered how in the hell is that possible you just might have given me the answer !
     
  18. ultraedge

    ultraedge

    Joined:
    Aug 3, 2013
    Messages:
    44
    Broncman, Check Whidden Gunworks website for the meplat trimmer. Gary
     
  19. aj300mag

    aj300mag

    Joined:
    Oct 24, 2006
    Messages:
    295
    .006" variance in case length...

    When you shoot the short cases a hard carbon ring fills up the space from the end of the neck to where the 45° angle starts. When you shoot one of the cartridges that is .006" longer it is the same effect as shooting a cartridge that is .006" longer then the chamber neck length (max trim length).

    Might not make a difference on a Helen Keller (2MOA "10" ring) targets, F-Class rings are a tad smaller. YMMV ;D
     
  20. Gonzos

    Gonzos Gold $$ Contributor

    Joined:
    Jul 3, 2011
    Messages:
    297
    I just can't stand to not trim after every firing with my ammo for my F Class rifles. I don't know if it helps but it makes me confident that I have done everything I can to make the cases the exact same length and to make sure the case mouths are square. On my hunting loads I am not quite so picky - but almost.
     

Share This Page