COL question

Discussion in 'Reloading' started by 400bull, Aug 30, 2011.

  1. 400bull

    400bull Well-Known Member

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    I am looking at trying some Nosler 140 Accubonds in a new Browning X-bolt 7mm-08 that I recently purchased. When I measure the Max COAL using my Stony Point COAL gauge I am coming up with a Max length of 2.905. This seems to be on the long side as I know a couple friends that have the X-bolt their Max COAL is under 2.850. Does these mean I just have a long throat in X-bolt? I usually start my loads at .015-.025 off the lands. I have never had a rifle that I could exceed the specs by that this much. If I am just on the long side what COAL would you start your load development at?



    400bull
     
  2. rscott5028

    rscott5028 Well-Known Member

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    The Stony Point COAL gauge measures from a datum line on the ogive that's similar to a typical minor diameter in a bore for your caliber.

    SAAMI specs for COAL don't address that particular measurement so far as I know.

    Bullets vary by Mfg in the design of their ogive and bullets with a production Lot and within a box will also vary. Hence, COAL with one bullet as measured in this manner will be different from one bullet Mfg to another.

    Production rifles should be chambered with similar reamers. But, you will still have production variances there. Plus, headspace in production rifles may vary slightly.

    All of this can stack up to some pretty large numbers.

    The purpose of the Stoney point gauge is to find a relative starting point for seating the bullets in your rifle. Then, it's up to you to perform load development to come up with the ideal seating depth.

    I don't see a reason to be concerned.

    -- richard
     
  3. Loner

    Loner Well-Known Member

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    I don't know where this knowledge got hidden over the years. COAL is for minimum
    length. They need to make sure you don't shorten the load up so much that you jack
    the pressures over what is safe. You can load as long as you your throat will allow, just
    watch pressures as you near the lands or touch them.
     
  4. rscott5028

    rscott5028 Well-Known Member

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    I don't think SAAMI has a "COAL" spec for cartridges that correlates directly to what you're measuring with the Stoney Point...
    http://www.saami.org/PubResources/CC_Drawings/Rifle/7mm-08 Remington.pdf

    For 7mm-08, MIN length from headstamp to bullet tip is 2.530" and MAX is 2.800" and that has more to do with fitting factory ammo safely in the magazine and chamber.

    There's also no discussion about the allowable shape of the ogive. Hence, VLD bullets touching the Lands often exceed the MAX spec for fitting in the magazine. As such, handloaders either use the rifle as a single shot or modify their magazine to allow for the extra long bullets.

    As you shoot, the throat errodes and you may need to move your bullets out a tad farther to maintain accuracy. So, comparing COAL for 2 or more X-Bolt rifles is hardly worthwhile unless they are practically new.

    -- richard
     
  5. 400bull

    400bull Well-Known Member

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    I am fully aware that the COAL listed in the reloading manuals and the SAAMI COAL are suggested lengths for factory rifles. I understand that when trying to achieve optimum accuracy the COAL used may not be the lengths suggested in the manual and that I will need to find out what works best in each of my rifles. What had me confused is all my other rifles I reload for including a 20 year old Win 270 I can usually find a COAL that the rifle is happy with, within +/- .030 from the COAL suggested in the reloading manuals. With my Browning X-bolt I am more than .100 from what my reloading manuals suggest and .040 from the longest I have seen listed on the internet. This just seemed extremely long for me, so I wanted to check with others to see what their thoughts where. From the sounds of it no one would worry about it and move on with load development.

    400bull