What is acceptable variance in length?

Discussion in 'Reloading' started by drenner43, Oct 24, 2013.

  1. drenner43

    drenner43 Well-Known Member

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    I have been reloading for a little while now but I would still consider myself "new" to reloading, especially precision reloading. For you experienced long range shooting guys, I have a few questions.

    What is acceptable as far as variance in length of prepped cases?

    What is acceptable for variance in length of loaded rounds?

    Thanks for the help.
     
  2. Mikecr

    Mikecr Well-Known Member

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    Prepped case mouths, as in fully fireformed, can vary +/-5thou(and clear of chamber end) without detriment. Shoulder distance bumped from fireformed needs to be tight at 1-2thou.

    Length of loaded rounds (COAL) is pretty much meaningless unless you're limited by a magazine. W/regard to accuracy, you need to hold cartridge base to ogive(CBTO) within a few thou.
     

  3. Broz

    Broz Well-Known Member

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    Are you measuring with a comparator? If not the measurement you are getting is just leading you astray.

    Jeff
     
  4. Black Tail Hunter

    Black Tail Hunter Well-Known Member

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    +1 on this. There can be a lot of variance from the ogive of the bullet to the tip regardless of bullet mfg. If you are concerned enough then buy an overall length gage and comparator. Figure out how far off the lands you want to start and load to that length. Or just load to whatever length will fit in your magazine and see how it shoots. but measuring overall length will likely drive you nuts.
     
  5. BrentM

    BrentM Well-Known Member

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    Only disagreement I have with this is that some mags will allow a significant amount of jamming into the lands. We know that this can cause problems when trying to remove a unfired cartridge and having the bullet pulled from the case and left stuck in the barrel.
     
  6. rooster721

    rooster721 Well-Known Member

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    Regarding overall length.. I have a little to mention

    I just finished up a new load (for a new barrel) and noted some differences in COAL and accuracy. But it had to do with seating depth, more than anything*

    Some of my brass (work hardening reasons) seats hard, some seats light, and the majority is somewhere's in-between... basically, for those that are inbetween and relatively consistent; I see 2thou max (difference) in seating depths. For those seating lightly (easier than the others) they seat deeper; even up to 4thou deeper than my 'good ones'! And finally, those tough to seat suckers, they seat up to 3 thou SHALLOWER* ...all that said, those (most extreme) differences in SEATING DEPTHs, (on my paper anyhow) showed 1/4" groups going to an inch (+) !!!

    I find, if you can keep seatings/& OAL (in regards to that and seating tenisons) inside of 2-3thou of whatever your most accurate seating depth is, you'll keep consistent loads. Once you're out of that 2-3thou window, (in my case anyways) you can kiss your accuracy goodbye..

    To fix all that, I'm going to be annealing from here on, in an attempt to eliminate or at least decrease those variances* See what happens. But should cure it.
     
  7. Gene

    Gene Well-Known Member

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    Trimming a batch of brass to the same length to the thousandths is near impossible. I try to keep them about .005" less than SAMMI. But I have some trimmed much less than that. This can give you inconsistent bearing surface, i.e., more or less time the bullet is in the bore affecting rotational spin. The further back you trim the greater the chance of developing a carbon ring at the leade.
     
    Last edited: Oct 25, 2013
  8. BrentM

    BrentM Well-Known Member

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    I prersonally believe this accuracy variance is the combination of pressure and depth. Perhaps that is what you are eluding to. I have played around with depths for a long time and did not see much change in spread via seating depth with a few thousands between loads. I do see issues with brass flex and neck tension and that is usually quite evident on the chrono. If the pressure spikes due to a tight neck or inflexible brass you could easly see a 50 fps jump. That is about like adding a full grain of powder to your case.
     
  9. boomtube

    boomtube Well-Known Member

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    What is acceptable as far as variance in length of prepped cases?
    What is acceptable for variance in length of loaded rounds?


    Depends on what you're willing to accept. If it was a specification it would be in all the books. ??
     
  10. rooster721

    rooster721 Well-Known Member

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    I think the real answer lies someplace between your opinion & mine, in all honesty. My seating differences (definitely) are being affected by the brass/each cases neck tension. So, probably has to do with the flex or lack-of flex that certain particular cases in the bunch have-- again, I am sure annealing is the answer to resolving a good part of that. If annealed, and softened (obviously to be uniform now) then tensions, and seating depth alike would be more uniform too.. and pressures, etc etc

    We'll see how it goes. In my opinion, I think in certain calibre/certain brass' case, annealing is the way around such variances-- time will tell
     
  11. Mikecr

    Mikecr Well-Known Member

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    You think annealing is free, but I doubt it.
    There are costs to everything.
     
  12. rooster721

    rooster721 Well-Known Member

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    I have a bench source Mike. It's far from free.

    The cases I shoot, generally speaking, are toast after sizing 4 times.. and I load for three particular rifles like that. So to a guy like me, a few dollars for a proper annealing unit is worth the cost. If I can squeeze a few additional loads out of my brass, PLUS gain in the accuracy/uniformity department, it's money well spent.. and if you want to look at it this way.. in the case of even ONE extra re-load outta my brass, by annealing, in time it will pay for itself* Think about that for one second.

    There ARE costs to everything, but when those costs are "positive costs" spent to work in your favor and SAVE you money in the long-haul, tell me how they aren't worth it..? To each his own I guess.
     
  13. drenner43

    drenner43 Well-Known Member

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    That's a very good point. I am not, I will be now though as I will be purchasing one. I am limited due to magazine length in this rifle. So I guess really this topic is kind of null and void unless I want to start using the comparator to measure and possible single shot.
     
  14. Broz

    Broz Well-Known Member

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    Not really. If you use the comparator, no matter what OAL, at least the bullet O-give will be consistent as far as distance to the lands on all rounds. You will then see that the rounds will all measure the same as you will be eliminating that .005" to .010" of variance in the very tip, that means nothing you. The end results will be that all rounds will have the same jump to the lands. I urge you to try this.:)

    Jeff