Chamber questions

Discussion in 'Main Message Board' started by afret, Jan 13, 2020.

  1. afret

    afret

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    With this info which one would be better for shorter FB bullets? I know a short freeborn would be good for this but what is the "throat"? Sorry for the format. I tried to space it out but it turned out like this.

    Chamber Reamer Dimensions

    Cartridge Neck F.B.L. F.B.D. Leade Throat Manufacture




    6mm BR Norma . 271 .094 .2435 .2387 .3465 JGS
    6mm BR Rem .271 .1163 .2435 .1001 .2302
    PTG
     
  2. DaveTooley

    DaveTooley Silver $$ Contributor

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    What FB bullets?
     
  3. afret

    afret

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    Berger 68 grain FB.
     
  4. geo.ulrich

    geo.ulrich beware of owner Gold $$ Contributor

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    the jgs is closest but .09 is still fairly long for a 68 gr. around .04-.06 would be best
     
  5. afret

    afret

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    Thanks! These are the two choices in prefit barrels by X-Caliber. I'm planning on shooting 68 and 80 grain FB Bergers.

    What if any is the relationship of freebore to the throat?
     
  6. geo.ulrich

    geo.ulrich beware of owner Gold $$ Contributor

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    If your going between 68 and 80 gr make sure you get a 12 twist the 80s won't work in a 13-14 twist.
     
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  7. afret

    afret

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    Thanks for the advice. Ordered a 12 twist. Just have to wait now to have fun. :)
     
  8. Dusty Stevens

    Dusty Stevens COVFEFE- Thread Derail Crew Gold $$ Contributor

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    Dont go with the br rem one. Besides the fb being too long its going to open up other cans of worms
     
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  9. LCazador

    LCazador Competitive shooter and reloader for 50 years+ Silver $$ Contributor

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    Done this! Ulrich right on!
     
  10. gunsandgunsmithing

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

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    I have a .098fb 6br Norma reamer and it's been a good one. It's just about perfect for the 80s and you have plenty in the neck with the 68 bergers. Some light fb and most boat tails...not so much the case.
     
    Last edited: Jan 13, 2020
  11. afret

    afret

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    Thanks everyone for the info and advice.
     
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  12. Ned Ludd

    Ned Ludd Gold $$ Contributor

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    Technically, the term "freebore" is the same dimension as the "lead". You may sometimes hear people use the terms "freebore" and "throat" interchangeably in conversation, but that is not correct. If you look at the reamer print below, you can see that the lead dimension is 0.085" (in red), which is also the "freebore"specified by this reamer. The throat, which is in front of the lead, includes the region from the start of the land angle onward. Effectively, the freebore (or lead) is the region in front of the end of the case neck, up to the start of the rifling, but that itself has no rifling. Hence the term, freebore, or bore that is free of rifling. In fact, the freebore will often be about half a thousandth or so over bullet diameter. Hope that helps.
     

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  13. afret

    afret

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    Thank you for the explanation. It's kind of confusing since it seems like the terms are used interchangeably by different sources. I saw some diagrams where the lead is the slightly angled section beyond the freebore .
     
  14. Ned Ludd

    Ned Ludd Gold $$ Contributor

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    I didn't want to add to your confusion, so I didn't mention the term lead angle previously. However - the lead angle is the specific angle at which the the lands rise up to their full height in the throat (i.e. right after the lead, which has no lands or grooves). This section in front of the lead where the lands begin defines the throat. On the reamer print I posted above, the lead angle is shown as 1 degree 30 (1.5 degrees), which is fairly common. Anyhow, not sure who came up with all this terminology - it was all done long before my time. But it certainly can be confusing, especially when it's not always used correctly.
     
  15. afret

    afret

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    Thanks again. Starting to make more sense now. :)
     

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