Measuring for a Reamer

Discussion in 'Gunsmithing' started by statjunk, Mar 26, 2010.

  1. statjunk

    statjunk Well-Known Member

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    Jul 15, 2009
    Hello All,

    I'm trying to build a rifle that is chamber in 300 WM where with a 180gr Accubond can load to the lands and still fit the rounds in the magazine.

    Can someone please describe to me how to measure what I'm trying to get to so that I can order the appropriate reamer/barrel?

    Thanks to all.

    Tom
     

  2. NesikaChad

    NesikaChad Well-Known Member

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    Jan 28, 2007

    Hi Tom,

    The simplest solution I've found is to load a sample cartridge to the desired length and then mail it off to David Kiff at Pacific Tool. Dave is the man and he'll set it up just the way it should be.

    Good luck.

    Chad
     

  3. statjunk

    statjunk Well-Known Member

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    Jul 15, 2009
    I'm not looking for an exact match or anything like that. I'd like to know what the measurement should be so that I can call around to see if any of the various barrel makers/installers already have a reamer that will work well enough.

    Any ideas how I can figure out what size reamer I'll need if I work up a dummy round?

    Thanks

    Tom
     
  4. NesikaChad

    NesikaChad Well-Known Member

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    753
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    Jan 28, 2007
    The "ideal" situation:

    1. Your magazine length is long enough to do whatever you want.

    2. If that is the case seat your bullet out to where the boat tail/bearing surface intersection sits just above the neck/shoulder junction of the case.

    Advantages:

    It keeps the bullet out of the "doughnut" ring that can (not always, but sometimes) cause variances in velocity and weird things on paper.

    It maximizes the powder column potential of the case by avoiding a seating depth that has a portion of the bullet squashed down where powder is supposed to be.

    Regardless of how you get there it should still start with a loaded dummy round because whoever chambers the thing is going to need some sort of reference. He may have the perfect reamer or may need to chase it with a throat reamer after the chamber is cut.

    Just be sure to qualify the COAL in the magazine box prior to any barrel work so that you don't end up with a chamber that's freebored like the "pivot girl" at the homecoming game.

    Good luck.

    Chad
     
    Last edited: Mar 26, 2010
  5. sdeering

    sdeering Member

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    Mar 14, 2008
    A few points some already mentioned.

    Stay out of dougnut.

    Should have one bullet diameter in case- .308 bullet should be seated in .308 or more.

    What you can do is load a round that just fits the mag- make sure you have more than .308 depth in case.
    Take you calipers and set them to .307 slide the calipers down the ogive of bullet till they touch bullet, this is where your lands will start to contact the bullet. You can turn the bullet lightly, making a very light scratch mark on it. now measure from the end of you brass to the scrach. This will be your freebore distance. This will get you close to what you need. You can shorten the dimension some to alow for throat erosion. This may not give you the (optimum round) but will give you mag fit and touching the lands.
    Stephen