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Reloading Berger Bullets

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bullet seating accuracy

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  #8  
Unread 08-25-2013, 12:44 PM
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Re: bullet seating accuracy

Quote:
Originally Posted by Mikecr View Post
What is vital to perfect seating though, is rational and consistent seating forces(another thread).
Bingo! Nuff said

What I always found incongruous is how the comparators from Hornady are .011" under caliber while the land size is typically .008" (from what I understand, correct me if incorrect) under.

Example .308 caliber comparator



Seems like if you were looking for a true distance to the lands a comparator that was land diameter would be more appropriate
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  •   #9  
    Unread 08-25-2013, 01:31 PM
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    Re: bullet seating accuracy

    Quote:
    Originally Posted by woods View Post
    Bingo! Nuff said

    What I always found incongruous is how the comparators from Hornady are .011" under caliber while the land size is typically .008" (from what I understand, correct me if incorrect) under.

    Example .308 caliber comparator

    Seems like if you were looking for a true distance to the lands a comparator that was land diameter would be more appropriate
    Well they've got to be a little smaller than land diameter or the bullet would slide right thru the comparator - no?
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      #10  
    Unread 08-25-2013, 01:47 PM
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    Re: bullet seating accuracy

    No, the bullet is BORE diameter

    Example: bullet .308", groove diameter .308", land diameter .300"

    So if you made the comparator .300" then it would hit the bullet ogive exactly where the lands would hit it

    Right?
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      #11  
    Unread 08-25-2013, 02:02 PM
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    Re: bullet seating accuracy

    Yes, you're exactly right. My bad. My mind replaced groove with land. Sorry.

    I always knew my hornady comparators hit the bullet farther from the lands than necessary, and what seemed more desirable. Just never measured them.
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      #12  
    Unread 08-25-2013, 02:10 PM
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    Re: bullet seating accuracy

    It isn't that simple, and yet simpler still.
    Throats are cut at whatever angle the reamer provides. It could be from ~.5 to 15degs.
    Bullet noses come in various forms(tangent, secant, hybrid) and radius ~8 to 15degs.
    Various combinations change the contact points of both lands AND noses.

    You can order your reamer with a throat angle that matches a particular bullet nose.
    You can have a comparator made with the barrel stub and same throating from that reamer at barrel finishing. Only this would provide for true contact datum from a comparator.
    Change bullets and you negate the efforts.

    But it doesn't matter, as a relative datum is typically what we define while discovering most accurate seating distance -with any particular bullet. You can log it, and as long as you always use the same tool & method of measure, then you can reproduce that best seating distance.

    I don't pay any mind to where a Sinclair nut contacts w/resp to loaded contact. I'm satisfied as it get's that I can reproduce with the nut whatever I measured with it as best seating.
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      #13  
    Unread 08-25-2013, 02:20 PM
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    Re: bullet seating accuracy

    But the bullets don't really exert back pressure from engraving forces until the bullet actually hits the beginning of the lands

    So isn't that the true distance to the lands?
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      #14  
    Unread 08-25-2013, 04:07 PM
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    Re: bullet seating accuracy

    Barrels were origionally bored and then rifled. Bore diameter is, by definition, the size hole that gets precisely bored during manufactoring, groove diameter is to the bottom of the rifling. Ergo, a .30 cal barrel is bored to .300" and, with a normal rifling depth of 4 thou, the groove diameter is .308".

    Seating a precise amount off the lands isn't the goal, finding the best shooting jump to the lands is but that's a relitive thing,it matters not if we know to the last thou what it really is.

    A seating variation of +/- 5 thou rarely matters unless we're seating on a ragged edge of what works well..
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