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Case length and brass trimming

Discussion in 'Handloading and Reloading' started by CJK8, Aug 27, 2011.

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  1. CJK8

    CJK8 Member

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    All the manuls I read show the brass with a length of 1.760 but tell you to trim it to 1.750. I don't understand why you are supposed to trim it down below 1.760. Could someone explain? Thanks.
     
  2. gennro

    gennro Member

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    Because the brass can expand after fired and this prevents the case from getting stuck in the chamber. Plus if the gun is dirty, out of spec, etc. This will let the round chamber successfully.
     
  3. gamestalker

    gamestalker member

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    Case length must be maintained at or below maximum to prevent the mouth and bullet from becoming pinched in the throat, thus causing pressures to rise excessively. This happens because the mouth can't expand suffciently to allow the bullet to exit before pressures exceed normal operating range becuase of the delay that is created. An easier way to explain this is to imagine what would happen if the bullet was not allowed to exit the mouth when it is supposed. Even a very slight interuption of mear miliseconds can be desasterous in this respect.
    A case that is too long is likely still going to chamber without noticable resistence or problems and is not a reliable means of monitoring or recognizing the need to trim. I watch all of my brass for SAAMI case length spec., but I am absolute about maintaining proper case length with bottle neck cases, as they are more prone to pinching than would be an AL or other straight walled cartridge is.
     
  4. CJK8

    CJK8 Member

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    I guess I should have mentioned the dimensions are for .223. So, does the brass expand that .010 each shot? If it doesn't, do you need to trim it after each firing? Thanks.
     
  5. gamestalker

    gamestalker member

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    Trimming is based soley on case length according to the maximum SAAMI spec.. If your brass is longer than the maximum as per SAAMI spec. then it needs to be trimmed to within the trim to length.
     
  6. cfullgraf

    cfullgraf Member

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    The short answer is "it depends".

    With 223 Remington, if you trim to the recommended minimum, you should get a few shots from the brass before you need to trim again.

    Heavy loads will probably need more frequent trimming. Some cartridges, by their design, just need more trimming. Light loads generally need less trimming.

    The case actually grows on resizing. If you measured a fired case, it may actually be shorter than before firing.

    Some folks like to keep their brass the exact same all the time, so they trim every time.

    I measure my cases every time but only trim those that are too long.

    If you are using a bolt rifle and neck size, your need to trim will be greatly reduced.
     
  7. Walkalong

    Walkalong Moderator

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    I have never had a .223 case grow .010 on one firing, but some soft cases can do it in two firings. Cases will grow the most on the first three or four firings or so and then slow down as they get work hardened. I used to check a batch of .223 brass after each firing and trim if any of them were over 1.75, but now I just trim them every time since I got my Possum Hollow trimmer because it is so easy. One of these days I may get a Giraud so I don't have to manually deburr and chamfer. :)

    1.760 is SAMMI max. Your chamber could be longer or shorter.
     
  8. CJK8

    CJK8 Member

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    I have some brass that is 1.755". Is that too long? How do I know what is too long? Thanks.
     
  9. dmazur

    dmazur Member

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    gamestalker answered this question, but it may not have been clear

    1.760" is SAAMI maximum length and 1.750" is the recommended trim-to length.

    If your case has grown larger than 1.760" through repeated firing and resizing, then there is danger of crimping the case mouth in the rifling, causing dangerously high pressure.

    Most use calipers or some kind of "drop-in" gauge and trim cases that exceed the SAAMI length. Most trim to the recommended length so they don't have to do it as frequently as if they trimmed to a longer length (but still less than SAAMI max.)

    Can you trim 1.755" cases? Sure. It isn't necessary, but it won't do anything except consume time.
     
  10. cfullgraf

    cfullgraf Member

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    dmazur's comments are good information.

    To add, in general, there is a published maximum length for cases. For a SAAMI accepted cartridge, all chambers cut to SAAMI standards should accept cases at this length without problems.

    Due to manufacturing tolerances, chambers may accept longer cases, but it is not a good practice to routinely allow cases to grow longer than this published maximum length.

    The rule of thumb is to trim cases to 0.010" below the published maximum length. This allows for a few to several reloadings before the case exceeds the maximum published length.

    Cases could be trimmed shorter, and a few thousandths of inch won't hurt anything, but again, it is not advisable to trim too short.

    Cases any where between the published maximum length and the "trim to" length (nominally 0.010" below the maximum) are safe and fine.

    Some folks like all of their cases trimmed exactly to the same length and trim them even if they do not exceed the published maximum length. There are valid reasons to do this for specialized purposes, including the reloader's preference. Generally, this level of precision is not necessary for most shooters.

    So, the short answer is, when a case exceeds the published maximum length, trim it. Trim it to no more than 0.010" less than the published maximum. But, not trimming to 0.010" less will mean you may have to trim more often.

    For non SAAMI cartridges there are no published maximum although the developer may have a figure in mind. It is best to have the chamber measured and make adjustments from there. Once a max length is determined, the 0.010" trim could be used.

    For me, I have cut a caliper like "go-no-go" gauges for my cartridges. The gauge is cut to a couple thousandths of an inch shorter than the published maximum. If a resized case fits the gauge, it does not get trimmed. If it fails to fit the gauge, it gets trimmed. A caliper could be used to do this measurement but I have a thing about handling precision measuring tools more than necessary. (Butter fingers, you know)

    Hope this helps and makes sense.
     
    Last edited: Aug 29, 2011
  11. Sensai

    Sensai Member

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    Good word Chuck. The only thing that I would add is that I keep my brass in "batches". These batches are normally sorted by manufacturer and number of reloads. When I get one or more pieces that need trimming, I trim the whole batch. This keeps the whole batch the same length, and aids in accuracy (at least in my mind).:)
     
  12. CJK8

    CJK8 Member

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    I think this means once fired brass that is 1.755" or 1.756" is fine to shoot since it is below the max of 1.760". Do I have that right? Or does it depend on the gun? If it depends on the gun, how do I know? Thanks.
     
  13. brickeyee

    brickeyee Member

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    Unless you have actually measured the chamber length (Sinclair has the 'buttons' you need if you cannot make them).

    Them you can set a trim length based on the actual chamber.
     
  14. dbarnhart

    dbarnhart Member

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    >>I think this means once fired brass that is 1.755" or 1.756" is fine to shoot since it is below the max of 1.760". Do I have that right? <<

    Yes, that is right.
     
  15. CJK8

    CJK8 Member

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    So then, what is the cutoff? If brass is 1.759", do I need to trim? 1.758"? I have a bunch of once fired brass and just trying to figure out which ones I can use without trimming as I try my first loads and am learning the reloading process. I haven't bought a trimmer yet. I will, but not before the fisrt loads if I don't have to since I have everything else I need. Thanks.
     
  16. Walkalong

    Walkalong Moderator

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    I would trim anything over 1.755. It will never hurt anything.

    On the other hand, lets say that your chamber is a hair short, and that 1.758 brass stretches to 1.760 upon firing. Hmmm.

    Just sayin', stay safe. :)
     
  17. CJK8

    CJK8 Member

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  18. Walkalong

    Walkalong Moderator

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  19. cfullgraf

    cfullgraf Member

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    Any cases longer than 1.760" needs to be trimmed for sure. Any less, not necessarily. Remember, cases grow on resizing.

    But, a SAAMI chamber could be cut short but that should be rare, I suspect.

    You could be conservative and trim anything over something less than 1.760". Walkalong chooses 1.755". I trim anything over about 1.758" for 223 Remington.

    As I said, I trim only cases over my maximum length. Sensai chooses to keep cases in batches and trims the whole batch when one case exceeds the maximum. Both are safe methods. We each have our reasons. Sensai's cases would be more uniform, and if nothing else, he feels better about his reloads and therefore he will shoot better. I hate trimming so I minimize what i have to trim.

    In my opinion, calipers are the most flexible for measuring over all case length. besides, they can be used for lots of other measuring chores. The cases gauges measure shoulder position and over all length, but you do not get a number.It is just a "go-no-go" indication. Tools such as RCBS Precision mic or Sinclair's bump gauge give better information than a case gauge.

    As a note, the bulk of the bottleneck case gauges on the market are not chamber gauges. A round can fit the case gauge but not fit your chamber. But that is another discussion.

    Hope this makes sense.
     
  20. Hondo 60
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    Hondo 60 Member

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    I trimmed all my brass to 1.750 after the first firing (of factory ammo).
    And I've used PPU, FC (civilian & mil spec), LC 05, 06 09, 10, Fiocchi, RP, plus a coupla others I can't remember off hand.
    I'm at a 6th reloading & all my brass is still shorter than 1.760
    So no, atleast so far, they haven't grown back that extra .010"

    This has all been fired outta my AR15A1.
     
  21. medalguy

    medalguy Member

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    I have a rule that if a case is longer than .005 below the max, I choose to trim it back to the .010 under max. That way I never have the concern of firing brass that just might be too long. Generally with moderate loads, I can get 3-4 firings between trimmings. For example, if maximum case length is 2.000 inches, and I have a case measuring 1.996, then I trim it back to 1.990 even though it is .004 under the maximum length.
     
  22. raddiver

    raddiver Member

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    I dont know if it helps the conversation or not, but tonight i was FLS some brass and decided to take a before and after measurement. 1.748 before 1.752 after. I measured about 5 of them and they all seemed to be in the .003 - .004 range.
    Also experienced my first stuck case but that's another rant.
     
  23. twofifty

    twofifty Member

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    is it true?

    Is it true that [in general] cases that are frequently trimmed end up with a shorter overall case life?

    As I understand it, trimming frees up space at the case mouth end of the chamber. The case, upon firing, will stretch out to occupy this space. So brass flows more 'quickly' from the case's base area to the case's neck, which thins the body above the case web...leading to eventual case head separation.
     
  24. rondog

    rondog Member

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    I bought a Giraud trimmer and have several thousand pcs. of .223 brass. I finally got them all cleaned, prepped and primed, and am working on getting them all filled up. No telling how long it'll take me to shoot them all up, if ever. So it'll be awhile before I have to trim them again!
     
  25. cfullgraf

    cfullgraf Member

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    Trimming, itself, does not shorten case life. Needing to trim cases frequently is an indication of something else that is shortening case life.

    These could be, but not limited to, near maximum loads and over resizing the case, such as moving the shoulder back more than necessary for the chamber.

    At the other end of the spectrum, neck sized cases rarely need trimming because the case is not worked in the resizer die.

    raddiver,

    Cases usually will get shorter on firing. The body of the case expands to fill the chamber and it pulls material back from the case mouth and neck. Also, the wall of the case also becomes a little thinner as the circumference of the body of the case gets longer. The brass has to stretch around its circumference, as opposed to length, to fill the chamber so it gets thinner.

    So, when the case is resized, the body is returned to about the original size, but the case walls do not get thicker again. The brass as to go somewhere, so it gets extruded up to the neck and makes the neck longer.
     
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