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Thread: Do you always need to case trim?

  1. #1
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    Do you always need to case trim?

    G'day team,

    I've got a question around case trimming I hope for some good discussion around.
    I've just got myself a case trimmer and trimmed up my latest batch of .308 brass. I have already loaded this brass and they have been fired twice.

    I was told the brass stretches most after the first firing. So basically this 'stretched brass' has already been into my gun and is fine. Even though it was about 3-4 thou longer than the max SAAMI length.

    I also load 7mm08 and have the same issue. The brass is longer than max but the loaded cartridge fits inside my weatherby mk 5 ultralight.
    However it doesn't fit inside my cousins new tikka t3.

    My .308 is a BSA CF2 and I have read that both the weatherby and BSA have quite a generous throat length. Whereas the Tikka is quite short.

    So basically, should I be trimming back to Max SAAMI lengths for my brass.
    Or do I need to spend more time trimming then working out the correct seating depth to reduce the bullet jump to the lands?

    Hope ive got that terminology right. I do have the Nathan Foster book and its awesome but unless I have read it wrong I can't quite understand this bit.

    Cheers
    Dan

  2. #2
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    Hi unless there is something wrong with your chamber or you are reloading to outlandish pressures there is no need to keep trimming. I check it a few every 3-4 loadings and trim if needed. I have some .223 Rem brass that hasn't been trimmed in 8 loadings and its still fine. Trimming your brass will not affect your loaded length as it is the seating die that sets the loaded length not the brass.
    I hope that semi clarifies things.

  3. #3
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    If you neck size particularly with a lee collett die then you don't need to trim as the brass doesn't get stretched.
    Feather or Shoot likes this.

  4. #4
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    I trim and debur every 3-5 loads some cals have more case stretch than others

  5. #5
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    I trim every third firing. After 3 shots, they've grown .005" to .010" and it seems to vary from one case to another.
    I trim to a length midway between SAAMI max and min. It's ideal if you choose a length that's short enough you trim a bit off every case so they are all the same.

    If you want to use the same brass in several guns then you should full length size them every time and keep the brass length within SAAMI range. You will also need to keep cartridge overall length within SAAMI spec and check you haven't seated the bullet into the lands for one of the rifles. This is more likely if you use a stubby round nose bullet loaded to max SAAMI COAL. Most factory chambers are set so you can't reach the lands with a spitzer or boat tail bullet at SAAMI max COAL (don't quote me on that its just my limited personal experience).

  6. #6
    P38
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    I trim mostly to ensure all cases are the same length.

    Haven't seen a 308 case that's over spec yet.

    Cheers
    Pete
    Arguing with an Engineer is like Wrestling a Pig in Mud.

    After awhile you realise the Pig loves it.

  7. #7
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    I trim every firing so I don't get a bur form if the case mouth touches anything it shouldn't. I keep an extra watch on that outer edge that you usually chamfer off. That one I tilt the chamfer tool over so the entire neck ends up perfectly smooth. You don't want anything stuffing up the alignment of the projectile in the throat.

  8. #8
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    Thanks Guys,
    Pretty sure I've got it.
    I only have a full sizing dies for both calibres. Looks like I don't need to be trimming back to max case length. At least for my rifles, each one is different. I'm going to do some loads for my cousin for his Tikka so will need to measure his Max COAL and go form there

    Just a little trim to tidy up any unevenness then a little chamfer in and out.

    Thanks heaps for your inputs.

    Cheers
    Dan

  9. #9
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    Greg Duley did quite a good write up on how to measure chamber length a few years back. Chamber length is different to throat length. Most chambers are longer than saami length, but how much varies from brand to brand and rifle to rifle.
    Do a search on "Chamber length gauge" if you want to buy one, but they are calibre specific. When I looked for one a while back postage was way more than the gauge.

  10. #10
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    Thanks Stug,

    Nathan Fosters book has a good technique that just uses a cleaning rod. I have done this on both rifles. I'm just learning the implications for the measurement and how it relates to everything. I obviously didn't get it when I went and trimmed the cases back to length.

  11. #11
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    @i41do2 How does he measure it with a cleaning rod?

  12. #12
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    I think you will find Nathan's way is for finding the lands.
    I use the Sinclair case length gauge. But still like to trim little and often to keep the neck square.

  13. #13
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    I think its actually max OAL, but anyway here it is.
    you need a long rod, preferably single section but with a male thread or solid end not a female thread.
    close the bolt on an empty chamber but don't pull the trigger i.e leave the pin retracted.
    run the rob in from the muzzle till it hits the bolt face. place a clothes peg against the muzzle. pull it out and mark where the peg is against the muzzle.
    that's your first point.

    Next remove the bolt
    get a projectile and push it in to the chamber till it seats on the lands. you will need to hold it in with another rod or similar. then place your original rod in to the muzzle till it sits on the projectile tip and place the peg back on. mark the point and then measure the distance between the two.

    Having just written that Its measuring the max overall cartridge length. But that's a start and you will be able to work out some other points from that I think.

  14. #14
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    heres a link I just found for a do it yourself chamber gauge
    How to Craft Your Own Chamber Length Gauge Daily Bulletin
    6x47 likes this.

  15. #15
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    Distance to lands measurement - LINKS

    Measuring the distance from bolt face to the lands seems to be rather imprecise. Variation from one attempt to another is typically 0.005". Usually it's recommended to repeat measurements several times and average.


    Wide ranging discussion. Cleaning rod method is outlined in the 4th post by "Woods"


    Shoulder to lands measurement @kimjon shows a home made device. This guy is a DIY mechanical legend (and expert hunter). He got very reproducible measurements with this.


    Comparison of "slotted neck" with "home made rod through flash hole" methods.
    i41do2 likes this.

 

 

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