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Thread: How important is case length?

  1. #1

    How important is case length?

    I've got a batch of norma brass which has been fire formed in my rifle but is all shorter than the standard Lee resizing tool (the small, handheld basic one), so no brass is being trimmed. Problem is that case length varies quite a bit (0.005 to 0.010") and they are all shorter than the Lee trimmer which means that when I compare finished lengths using a comparator the bullets will all be seated fractionally different amounts (in order to get the same overall length).

    How much is acceptable in difference in case length and should I buy a proper resizing kit and take all the cases back to a consistent, but shorter length?

  2. #2
    1: as long as the cases are not longer than the book figures or your lee trimmer, then its ok from a safety PoV. I have exactly the same thing with my 7-08 and nosler brass.

    Regarding consistency, well depends what you want.. It will have an affect, whether its noticable or not is another thing. I have 20 cases which i prepped to be as tight tolerances as possible. all are the same length +/- 0.002'' and all weigh the same. They all have the same neck wall thickness by neck turning and to be honest i dont notice a difference between those any my standard cases.. although my standard cases are similar tolerances to what you mention on length but are neck turned and weight batched.

    If it pleases you to be as accurate as you can, do it.. then you can rule out that variable when shooting. If it doesnt really bother you, forget about it!

  3. #3
    Thanks FF!
    Being slightly anal, I will probably do it to rule it out If the case lengths differ by 5 to 10 thou then that means my bullets will be seated different lengths by a similar amount, which kinda makes it pointless trying to get overall lengths to within +/- 0.002" (which is what I aim for!).

  4. #4
    well if your using the comparator, then your measuring from the head of the case to the ogive, and that will be consistent, so distance to the lands will be the same..

    the only thing is that there will be more or less bullet in contact with the neck walls which will alter pressures maybe?

    im with you, do it and rule it out.. i also check my ogive length to +/- 0.002 which takes time but is worth it in my eyes. The biggest increase in accuracy and ES etc came from using bushing dies and altering neck tensions though.
    Last edited by flyingfisherman; 07-03-2012 at 09:39.

  5. #5
    I would say that my Lee Case trimmer has only actually trimmed about 5-10 cases out of over 200 on my norma 270 brass, so over 95% are under the max length.

  6. #6
    I ran some figures through QL and as a rough guide for each 1.0mm difference in case length there is a 15fps gain or drop.
    Whilst this is not a replacement for testing over a chrony it could be a help in working out what to expect performance wise.

  7. #7
    cooter.. does QL also allow you to look at neck tension? Would be interested to see what it says!

  8. #8
    Yeah, that's my thinking, +/- 10 thou less or extra bullet in contact with the neck walls is likely to make a difference (or at least it will in my head )

    All the Norma brass I have (including once, twice and 3x fired and original Norma factory loads, unfired) averages around the 2.027" mark, which is right at the bottom end of the .243" case length range I've got in the relaoding manual of 2.025" to 2.045". Guess I'll be cutting it all back to 2.025" and working from there!
    Last edited by 75; 07-03-2012 at 10:11.

  9. #9
    Quote Originally Posted by flyingfisherman View Post
    cooter.. does QL also allow you to look at neck tension? Would be interested to see what it says!
    I don't think so, or at least not that I can work out. bobjs might know better.

  10. #10
    Is it not strange that the major ammunition companies cannot seem to make cases that are actually to the design specs?

    Surely tis not that hard a thing to do.

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