Case lenghth measurements? THAT important???

Discussion in 'Reloading' started by joshua99ta, Jan 19, 2010.

  1. joshua99ta

    joshua99ta Well-Known Member

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    Guys I was just wondering... I'm about to start working up some 30-06 loads w/ some 4831 and some 180 bergers... and I'm seeing a good bit of case length differences. ALMOST all of my once fired 7mm RUMs are 2.850, with a few @ 2.845s. These 30-06 cases are ranging from 2.490-2.509. All sized with the same dies, now not all were fired from the same gun though.

    I never even purchased a case trimmer, b/c of the consistency of the once fired 7mmRUM brass. Now to me just looking @ the case trimmers it looks like its going to be hard to get every single case the same lenght without repeatedly checking, and IF you do slip up and cut one a little too much it looks like your gunna start BACK over... IF you have racked up about 50-60 brass, I guess you can set that case out... BUT I like to work in even numbers! lol

    I'm gunna order myself a case trimmer this week anyway.
     
  2. MagnumManiac

    MagnumManiac Well-Known Member

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    It IS important that you keep your brass trimmed to below MAX length, it is a safety feature of the brass.
    Now, you probably won't run into trouble until your brass grows to around .020" over max length, but not always!
    I have a couple of rifles that show 'crimping' when they're only .005" past max length!
    This is why it's recommended to trim your brass .010" BELOW max case length.
    30-06 brass tends to stretch/grow quite a bit on each firing, so it's wise to check them often, you can trim ALL your brass to min spec when you get it, no matter what the initial source.
    I normally fire new brass first to iron out any shortcomings such as growing longer on one side and the like, then trim to MIN spec (.010" below MAX.).
    2.490" for 30-06 brass is MAX, you really need to trim them back to 2.480" to be on the safe side, the brass you have that measures 2.509" is way over max and needs to be trimmed!
    If you do not understand the reasons for this, get yourself a modern reloading manual, they will explain why it's necessary in detail!
    gun)
     

  3. boomtube

    boomtube Well-Known Member

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    Last edited: Jan 20, 2010
  4. fj40mojo

    fj40mojo Well-Known Member

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    I don't buy factory ammo for my center fire rifles but generally I treat virgin brass and once fired the same. Size and trim then fire and reload until it approaches or exceeds max length and then trim again. Yes, it is important for safety plus it is one more variable that is under your control. Remember consistency=accuracy.
     
  5. Stormrider

    Stormrider Well-Known Member

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    Or you can buy the RCBS X Die and trim only once. I've not had any cases grow since I got the X Die.
     
  6. Chas1

    Chas1 Well-Known Member

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  7. joshua99ta

    joshua99ta Well-Known Member

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    thanks fellas.

    I was just wondering. I know the manuals state to trim. I was just wondering if it was such a big deal to have them all within .001 or .002 of each other. I'm not just really worried about the accuracy with this rifle, its more of a b/s rifle that I'll take for under 300 yard stuff. It shoots pretty good for a semi auto(browning bar)
     
  8. Chas1

    Chas1 Well-Known Member

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    I'm assuming your question is after you trimmed them if so then .001-.002 of each other is ok.
     
  9. 41mag

    41mag Well-Known Member

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    IF loading once fired cases I always size them first, then if more than a few are on the upper end of the length, I will run them all through my trimmer set to 2.484". Some have a goodly amount cut some do not even touch, but overall they will all still shoot well within the accuracy levels of my rifles, and me on most occasions.

    On new cases, I run them through the sizing die just enough to allow an 1/8" or so of the neck to get sized and straighten any imperfections out. Most I have found are generally under the minimum length when measured so I will load them up as usual, and check them all after firing as noted by MagnumManiac. Even then after sizing some will remain at or under the minimum length, depending on the load.

    Bottom line with trimming is to keep the neck from being to long and getting crimped when your bolt closes on the chamber. The other is consistency. In some rifles you might see a big difference with them all being withing .002 - .005" of each other, in some depending on the load, you might not even notice a .010" spread with regards to groups, as long as you not squeezing the neck into the bullet in the chamber.

    One other thing I did want to point out, and this just comes from past experience with an auto loader, you might want to look at another powder in the mid range burn rate instead of 4831. Check powders that work well in the M1 Garand, and you will be way ahead of the game. What you will find using the slower powders is the bolt will get slammed back MUCH harder with the pressure from the slower powders, than when a faster powder is used. Something along the lines of 4895 or similar might be a better choice. The one time I loaded for an auto was for a Remington and it almost was bad from the get go using 4831. Do a little checking around I know some manuals list loads specifically for the Garand and these would be a good starting place. Here are just a couple, Speer No. 13, Hornady 5th Edition.

    One last thing on an auto loader, is you MAY have to use a small base die to get the fired cases to chamber reliably, especially when using brass fired in other rifles. Sometimes when fired they have a belly on one side from laying in the chamber. While this is no problem at the time, it may cause the reload to jam when loading from the magazine as the belly is now out of round with the chamber. Just a thought and something you might run into. If you notice jams I would look into picking up a SB sizing die.

    I wish you well with your loads, and these were just a couple of things I have had issue with through the years. Just throw out a heads up before you load up a hundred rounds only to find they aren't going to work in your rifle.
     
  10. Gene

    Gene Well-Known Member

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    It is better to trim them too short than let them get too long. Trimming to .010" or .020" below SAMMI is fine. There is one instance where exact trim length is important, and that is if you ever turn necks. Here, trim length will determine where the mouth stops, and the cut into the shoulder should be within .0001".
     
  11. Mikecr

    Mikecr Well-Known Member

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    Where did you get this nonsense from?
    I don't even use a stop for turning. I run up on the shoulder 'a bit' that is sufficient to eliminate donuts on fireforming.
    Now, if your cutter angle is a great deal different than your shoulder, a rational limit is appropriate. But one-ten-thousands is absolute rubbish..

    As far as trimming, I find no benefit in even checking much less doing it. If the brass fits in the chamber without crimping at the mouth, it is long enough and not too long. I've spent a good deal of time actually MEASURING neck tension, and found what anyone would guess; A few thou more or less of partial neck sizing changes nothing compared to typical springback variance in the ~half neck sized.
    It's just nothing to fuss over.
     
  12. bigngreen

    bigngreen Well-Known Member

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    I don't know if I quit understand, if your chamber is tight and your brass doesn't move then this may be cool but I have had several hunting rifles that move enough when firing that your method of checking length would cause serious accuracy issues at best and severe pressure problems at worst.
    I'm just a little confused maybe.
     
  13. Gene

    Gene Well-Known Member

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    I don't know any competition shooters who run up on the shoulder "a bit" without using the stop. To simply guess where you should stop creates inconsistency. Cutting further into the shoulder angle produces a deeper cut, weakening the brass. Why would anyone want to do that? You can do it your way, I will stay with mine.
     
  14. Mikecr

    Mikecr Well-Known Member

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    BigGreen, it's true that none of my cartridges grow. Right now I shoot 223, 6br, 6xc, 6.5wssm. If your cartridges do, then of course you will have to trim to stay clear of chamber end. If you look at your fired brass for shiny mouths, you can see such a condition coming on..
    All I'm saying is that precision in this isn't necessary. Sufficient is good enough.
    It will not cause accuracy issues or severe pressure problems, unless you let it get way outta hand.


    And Gene, Same with turning onto shoulders. There are no neck-shoulder junction concerns, or uses, beyond donuts and potential initial headspacing. With the correct cutter angle anyone could turn needed amount of the first 1/8" of shoulder. Thats One Hundred and Twenty Five Thousanths..
    I don't cut anywhere near that far down. I don't need to. But wildcat forming might require it, and if so, there is nothing wrong with it.
    Nobody can tell you how much you need to go up on a shoulder. There is no spec or standard for it. You might not need to at all, or stop at a point before reaching the shoulder. Just depends on what your needs are.
    On the flip side, I'm not suggesting anyone with a wrong cutter dig it into their shoulders to cause separation. Such a lack of common sense cannot be acounted for in my perspectives.