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Finding the right COL for 30-06

Discussion in 'Handloading and Reloading' started by bison, Feb 26, 2010.

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  1. bison

    bison Member

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    I'm a newbie and am starting to load for my 30-06 but am confused about what COL to use.

    For 165g Hornady Interlock SP's the manuals and Hogdon web site give me a COL of 3.30 (the Lee manual says this is the minimum COL). However, if I make a dummy bullet to measure the actual length of my chamber (close the action allowing the bullet to move with little friction in the neck, then measure) I get 3.24", so less than the 3.30 recommended.

    I understand that some 0.010" less than this length is ideal-ish for the "jump", so that would put me at 3.14", even shorter. I measured some factory loads (150gr Fed Premium with Sierra Gameking) and they were 3.17".

    So what COL do I use?

    thx
     
  2. 1 LT MPC

    1 LT MPC Member

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    Barnes manual lists c.o.l. of 3.218 for the 165 gr TSX boatail,
    3.205 for the 165 gr MRX boatail,
    3.225 for the 165 gr BND spitzer.
    I'd go with what the bullet maker suggests as a start. Best to use a guage for your bore though. Did you make a dummy at 3.30 and try it? What was the minimum col in your book? Minimum c.o.a.l. for 30-06 according to Barnes is 2.940, max is 3.340.

    Hope this helps.
     
  3. USSR

    USSR Member

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    There is no "minimum" COL, unless you have the bullet ogive contained within the case neck. The COL of 3.30" is simply the COL they used to obtain the reloading data. Use a shorter COL if you wish, although the charge weight data listed in the manual would not necessarily apply. I'm curious as to what rifle you have with such a short throat?

    Don
     
  4. 1 LT MPC

    1 LT MPC Member

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    "There is no "minimum" COL, unless you have the bullet ogive contained within the case neck."
    Hmm, seems to me to be a minimum C.O.L.
     
  5. mkl

    mkl Member

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    If your bullet is touching the lands in your rifle at 3.24 inches, I sure would not seat the bullet farther out than this. Personally, I'd go with your 3.14 inch OAL and see how that worked.

    Not all chambers are identical, and it would appear that the leads in your chamber are a little closer in than the rifle used in the Hornady loading book.

    Although some shooters load with the bullet touching the leads (lands), I know of no one who recommends cramming the bullet a few thousands into the leads.

    Just be sure your 3.24 is correct. You may want to make up a dummy at that length, smoke or magic marker the bullet and see if you get marks from it contacting the leads in your rifle when you chamber it. If you get marks, be assured your measurement is correct.
     
  6. NCsmitty

    NCsmitty Member

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    Be aware that different bullets will require a different COAL due to the profile of the bullet that you are using. If you change bullets, you need to set the contact point for that bullet too.
    Your math is off using the 165gr Interlock. The 3.24" dimension that you got, less .010 clearance is 3.23".
    I prefer .020 off the contact dimension but that's just me.
    You need to either make a dummy round as you have or make a reference in a log book or a combination of both. I make a note in my Lee Shooter computer program and I mark the box of bullets accordingly.



    NCsmitty
     
  7. bison

    bison Member

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    Thanks guys - Don my rifle is a brand new Win M70. So I will make a dummy at 3.24" (actually it was 3.245") and see if I get marks from contact with the lands. If so, I'll back off 0.010" (thx NCsmitty for the math correction) to 3.235" and see what happens.

    Much appreciated gents -
     
  8. rg1

    rg1 Member

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    Hornady's overall length of the 30-06 with the 165 BTSP and SP is 3.230" as tested in their manuals. Don't know where you got the 3.300" length?
     
  9. bison

    bison Member

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  10. rg1

    rg1 Member

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    3.230" will put you from .030" to .050" from the lands in most production rifles I've seen. All can be different. The Hodgdon and Lee info for that bullet is long at 3.300" even though the maximum overall length is 3.340" for 30-06.
     
  11. win308

    win308 Member

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    As long as you can get it...and have it still feed from the magazine.
     
  12. USSR

    USSR Member

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    bison,

    Never heard of a factory .30-06 having that short of a throat. I will be surprised if your dummy cartridge at 3.24" makes contact with the leade.

    Don
     
  13. rcmodel

    rcmodel Member in memoriam

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    You better look again.
    Lee doesn't even bother to tell you what bullet they are talking about.

    The only 165 grain 30-06 Hodgdon shows is for a Sierra SPBT bullet.
    That is not a Hornady 165 Interlock.

    Hornady manual gives a OAL of 3.230" for that bullet.

    The devil is in the details, and the details of what bullet the data is for is critical.
    The difference in bullet ogive accounts for the difference between Sierra & Hornady bullet seating length.

    rc
     
  14. bison

    bison Member

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    Thanks all for comments and clarifications - takes a while to get used to terminology, etc. I loaded a bunch up at 3.23" with various loads of powder and now just need time to get to the range! Busy with NRA instructor certification this weekend.
     
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