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Thread: COL Cartridge Overall Length

  1. #1
    Join Date
    Jun 2007
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    Alfreton
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    4,970

    COL Cartridge Overall Length

    as it may stop the same questions being asked over and over again


    The Carolina Marksman's Newsletter (07-25-10)


    Thanks for keeping up with The Carolina Marksman. The Carolina Marksman is a small business dedicated to the shooting sports, the pursuit of maximum firearm accuracy, and a general love of the outdoors.


    Article of the Week

    COL

    COL, cartridge overall length, is a measurement that all handloaders are familiar with. It is the measurement of a loaded round from the tip of the bullet to the case head. Adjusting this length can be good or bad depending on what your needs are.

    This measurement can be tricky to pin down exactly. If you were to measure 10 different rounds from the point of the bullet to the case head you are very likely to wind up with 10 different measurements. The reason for this is in the bullet itself. When a bullet is made (by the swaging process, as most are) a copper cup and lead core are pushed into a forming die at very high pressures. The copper and lead squeeze together forming the ogive and bearing surface, but the tip gets little attention in the process. The bullet is usually popped out of the forming die by a little wire into the point (the meplat). This is the reason that match hollow points are even hollow points, that little wire pokes a hole into to the thin copper jacket upon removal. When finding my COL I usually take an average of 10-15 rounds as my measurement. The only way to get a consistent measurement of COL is to use a tool called a comparator. This tool measures on the ogive of the bullet.

    COL can change a lot of things, and if your not careful it might surprise you. Changing the COL of a cartridge will move the bullet closer to or further from the lands (the part of your barrel where the rifling actually begins). It is generally accepted that you want the bullet fairly close to the lands for maximum accuracy, somewhere between approximately .050" away from (jumped) and .025" into (jammed, do this with great caution and never on hunting ammunition!) the lands. The further a bullet has to jump before engaging the rifling the more opportunity it has to become off center, this promotes inaccuracy. If a bullet is jammed into the rifling it can cause very high start pressures and may unseat should the round be unchambered. The most important things are to find what your gun likes best, what chambers and unchambers smoothly, and what feeds into and out of the magazine if you are using one.

    Not all guns have chambers that allow for bullets to be seated close to the lands. In my Remington .308 a Sierra 175 gr Matchking is a full .200" away from the lands when seated at the factory recommend COL of 2.800". (Remingtons seem to be much worse about long throats then other gun manufacturers, and that's coming from a guy who loves Remingtons.) Most of my ammunition jumps about .1" before it hits the lands, and even having that working against me I manage to shoot a .9 moa average consistently. It's all about finding what works in your gun.

    One thing to watch with COL is changing bullets. This is especially important when you are feeding from a magazine. I have been loading 180gr cast lead bullets in my .40 S&W for a while, and recently tried some 180 gr plated bullets. The new bullets have a different nose profile on them, and this changed the COL when loaded at the same setting on the die. The plated bullets no longer chambered in the gun, in fact they wouldn't even slide out of the magazine when I tried to remove them by hand. This same problem can happen in any gun with a magazine. You can imagine my surprise when I got out to the range and couldn't shoot my pistol.

    COL can work for you or against you, but so long as you understand it you will come out ahead.

  2. #2
    Join Date
    May 2000
    Location
    Very southeast
    Posts
    44,219
    I tend to agree with most of that

    I can never understand why some reloaders start adjusting charge weight before COL as the COL makes most difference on most factory rifles, get that right with chosen bullet and then start charge weight testing

    And buy a decent comparator, use Ogive to measure best distance to lands
    Baz
    ____________________________
    Accuracy is everything!

    http://www.wildcatrifles.co.uk/

  3. #3
    Join Date
    Jul 2002
    Location
    Carlisle, Lakes UK
    Posts
    2,627

    Thumbs up

    Quote Originally Posted by baz View Post
    I tend to agree with most of that

    I can never understand why some reloaders start adjusting charge weight before COL as the COL makes most difference on most factory rifles, get that right with chosen bullet and then start charge weight testing

    And buy a decent comparator, use Ogive to measure best distance to lands
    Absolutely, couldn't agree more
    Marksmanship = Accuracy, Consistency, Observation and a little of The Force
    SharpshootingUK http://www.youtube.com/channel/UCuNM...ew=0&flow=grid

  4. #4
    Join Date
    Oct 2010
    Location
    richmond
    Posts
    69

    Reloading

    I fully agree with all the above. i am currently going through load testing based on the COL and different bullets.
    Keep shooting

  5. #5
    Join Date
    May 2011
    Location
    Bedford
    Posts
    87

    oh dear...

    Just spotted this....


    When a bullet is made (by the swaging process, as most are) a copper cup and lead core are pushed into a forming die at very high pressures. The copper and lead squeeze together forming the ogive and bearing surface, but the tip gets little attention in the process. The bullet is usually popped out of the forming die by a little wire into the point (the meplat). This is the reason that match hollow points are even hollow points, that little wire pokes a hole into to the thin copper jacket upon removal.
    The reason match hollow points have hollow points is because the core is seated from the front of the bullet, this has nothing to do with ejector punches.

    'comparators' are the new fad.
    Simply check the overall length of a bullet from your selected manufacturer then check them all again with your comparator, you will find that you still measure differences!

  6. #6
    Join Date
    May 2012
    Location
    lincoln
    Posts
    116

    COL

    HI, Most factory build rifles will vary in chamber size unless you have a blueprinted action. I always check the aol before reloading and make sure the bullet head is 2 thou at most from the lands. this has given me fantasitc groups with the right weight charge for weight, speed, rifling. LIfe without the barrel harmonics putting the groups out is great.
    Shoot straight and safe , Monty57.

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