Freebore ,throat and leade

Discussion in 'Gun Project Questions & Gunsmithing' started by muleman69, Oct 20, 2019.

  1. muleman69

    muleman69 USMC -1st marine Div. RVN Gold $$ Contributor

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    Can anyone explain to me what each of these do and where they are in relation to a chamber? If one extends his freebore does he need to lengthen leade? Bit confused with a lot of this and would like to no as I read a lot on this forum about the throat,leades etc.
     
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  2. 243winxb

    243winxb

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    Freebore -right in front of the chamber. Same diameter as the barrel groove, plus a hair larger. Allows the bullet to chamber , with out hitting anything. When longer, it reduces pressure.

    Throat is the funnel part. Guides bullet to the leade.

    Leade- is the angle cut on the lands/grooves. Allows the bullet to engauge the lands with less damage. A swaging effect.
    REAMER6.png

    But i may be all wrong. Not a gun smith.
     
    Last edited: Oct 20, 2019
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  3. tobnpr

    tobnpr

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    Throat in the diagram above is another term for leade.
    "Throating" is a term used to lengthen freebore for heavier (longer) bullets by reaming the leade further up the barrel to get the desired additional length before the bullet engages the rifling.
     
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  4. muleman69

    muleman69 USMC -1st marine Div. RVN Gold $$ Contributor

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    So basically throat leade and freeborn are much the same?
     
  5. DaveTooley

    DaveTooley Silver $$ Contributor

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    No
    Picture a funnel with straight sides then a taper.
    The straight sides are the freebore. Usually a fixed diameter.

    Example 6.5 Creedmoor. Bullet diameter is .2640".
    The freebore diameter is .2645"
    In describing the throat area to a reamer maker the next number would be the length of the freebore section. For the CM it's .1992"
    Then the leade angle which is 1'30"

    So to summarize the throat would be
    .2645" X .1992" X 1'30"
     
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  6. muleman69

    muleman69 USMC -1st marine Div. RVN Gold $$ Contributor

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    Thanks ,Think I'm getting it figured out. So how much freebore diameter over bullet diameter should there be in a hunting rifle? Does leade angle change with different calibers?
     
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  7. DaveTooley

    DaveTooley Silver $$ Contributor

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    I hate to say this but it depends on caliber, use and the end user. I have some unusual customers so I engineer things so as not to violate rule #1. That rule is don't do anything to make the phone ring, get anyone injured or killed. 100% reliable function is paramount.
    I like .0007"-.0012" clearance. The bigger the cartridge and the less sophisticated the customer the larger the diameter to allow for carbon build up. Also not all bullets are "on size". Some are a bit fat.
    Leade angles, as spec'd in https://saami.org/ do change from cartridge to cartridge. Most smiths have settled on 1'30" for custom made reamers. Steeper angles can sometimes lead to accuracy issues.

    There's a wealth of information on the SAAMI website
     
  8. dmoran

    dmoran Donovan Moran Silver $$ Contributor

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    FreeBore-Leade1a.png
     
    Last edited: Apr 6, 2020
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  9. muleman69

    muleman69 USMC -1st marine Div. RVN Gold $$ Contributor

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  10. rammac

    rammac

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    Freebore and throat are NOT the same thing, they are lumped together by some people because they aren't aware that some chambers actually a have tapered section forward of the freebore (and before the lead) and that tapered section is the throat. The throat's purpose is to help center the bullet to the bore and if your chamber has a throat then you'll find that it probably has a very small taper of 1.5 degrees or so. If your chamber hasn't got a throat it's probably because skipping that tiny taper saves money on cutting the reamer and the lead (the tapered entry to the lands) is thought to do the same job as the throat.
     
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  11. Link

    Link Silver $$ Contributor

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    Is the angle of the lead in the print misleading? The taper of the red line looks backwards to me.

    TY Don
     
  12. tobnpr

    tobnpr

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    How so? You're going from no rifling where the freebore ends, ramping to full rifling at the end of the leade.
     
  13. Will Henry

    Will Henry

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    I have always just considered throat length the be the length from the front of the neck to the top of the lands. In other words, freebore plus leade. This may be right or it may be wrong but it's my way; so there! WH
     
  14. gunsandgunsmithing

    gunsandgunsmithing The best tuners and wind flags on the market Gold $$ Contributor

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    For simplicity...
    Lead=tapered section
    Freebore=straight section behind lead
    throat=both combined, i.e...a throating reamer cuts both at the same time. The lead is set but the freebore is dependent upon how far you run the throater in.
     
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