Extending Freebore

Discussion in 'Gunsmithing' started by cjuve, Oct 17, 2018.

  1. cjuve

    cjuve Well-Known Member

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    I am looking at having a couple reamers ground with custom throats to extend freebore to fit specific bullets. I am wondering if anyone has had negative experiences when extending freebore other than the obvious magazine length issues.
    The 2 calibers in question would be a 300 RUM and 338/300 Ultra Mag. I have done this before with another caliber and have seen no downside I was just wondering if others have had any issues with this?
     
  2. J E Custom

    J E Custom Well-Known Member

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    Extended free bore can be your friend if done right. Free bore can lower pressure and increase velocity, Especially in the large over bore cartridges.

    You can have two much if the wrong bullet is used, but generally if you load to mag length allowing the bullet to jump a little before it engages the rifling lowers the initial pressure spike making for easier engraving of the bullet.

    All of my wild cat designs have generous free bore and have exceeded
    Velocity expectations with lower pressures. Accuracy has been very good with all of these rifles.

    Just My experience

    J E CUSTOM
     
    L.Sherm, EddieHarren and just country like this.
  3. cjuve

    cjuve Well-Known Member

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    Thanks J E that is what I was kind of expecting to hear. I have 3 dummy rounds made up with my bullet set in the case where I want it waiting to be sent off. On top of that measurement I plan to add an additional .015 to the freebore to give a little more breathing room.
     
  4. MagnumManiac

    MagnumManiac Well-Known Member

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    I have an Edge, with my 700 mag box I am restricted to 3.6”, but with the bullet I use (300gr Berger OTM) I need to load to a COL of 3.740” to have the bullet shank level with the neck/shoulder juncture.
    My throat is cut to suit this, so I would suggest you do the same. My throat can also suit the 285gr Nosler, amongst others.

    Cheers.
     
  5. cjuve

    cjuve Well-Known Member

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    Thanks!

    Yes, I am fairly familiar with the positive side of increased freebore I was just wondering about the negative side. In my heavy 338 edge+p I load to a 4.050 coal with the 300’s and with a low end load of 94.5 gr of h-1000 end up with a velocity of 2925 FPS. I have also learned the hard way about the effects reduced freebore with a 7 RUM that was set up with .150 freebore. I was just looking for others that may have had different experiences than myself.