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Determining Neck Diameter

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  #1  
Unread 03-24-2008, 05:16 AM
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Determining Neck Diameter

I'm building a 6.5 Ruger and plan on using 7mm Dakota brass. I expect I'll have to ream or turn the necks, even more if I have to use 375 Ruger brass. From what I'm reading on a thread search for neck turning .011 for neck thickness is a good average. Reamer drawing shows the neck cut at .298 so with a bullet diameter of .264 plus a neck wall thickness of .011 a loaded case should be .275 with a .023 difference. Is there a rule of thumb on minimum for the case to expand on firing.

A little help in the procedure and equipment needed would be a great help.

Thanks in advance for the help
Jim
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  •   #2  
    Unread 03-24-2008, 06:19 AM
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    Why do you assume that neck turning is needed?
    Is the brass .017" thick?

    .264 +(.017x2) = .298
    A .298 reamer will likely cut ~.300

    Absolutely no way should you turn to .011 and create all that clearance.
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      #3  
    Unread 03-24-2008, 11:20 AM
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    Max brass OD (with bullet) should be considered to be chamber dia. minus clearance (usually 0.003" min.). Outside turning of the brass is usually the preferred method for reducing brass thickness and uniforming. For accuracy, most prefer a handheld tool. Reaming is good for bulk metal removal and the elimination of donuts as they form. With your specs, a neck thickness of 0.015" would be close.

    It appears that your calculations do not allow for two thicknesses of neck metal.

    Last edited by Winchester 69; 03-24-2008 at 11:27 AM.
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      #4  
    Unread 03-24-2008, 11:29 AM
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    Well first thanks Mikecr for correcting my oh so good math skills. I should have added two wall thickness'. da! What I'm getting at is when does it become necessary (safety factor) to neck turn. I have used 30-06 brass for a 25-06 quite often, but they were factory barrels and chambers. I've used 375 H&H for my 358 STA before I knew I could have problems but had none.

    Is there a minimum for clearance???

    Thanks
    Jim
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      #5  
    Unread 03-24-2008, 11:36 AM
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    Win 69, thanks.

    As Mikecr says the reamer will probably cut .300 for a chamber. Asking the gunsmith to determine this will be a good start, yes??

    .003 min. that's what I'm looking for and necks maxing out around 0.015.

    Thanks again guys
    Jim
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      #6  
    Unread 03-24-2008, 04:49 PM
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    Asking the gunsmith what you'll end up with is right. He'll know.

    My thing is minimum clearance, for minimum sizing.
    As said, .003 is pretty normal and fine.
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      #7  
    Unread 03-24-2008, 04:57 PM
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    .003 min. that's what I'm looking for and necks maxing out around 0.015.

    Thanks again guys

    i would say you have the correct numbers for both.
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