Some glosarry of terms: please will you help me

Discussion in 'Reloading Forum (All Calibers)' started by Campbell, Mar 12, 2018.

  1. Campbell

    Campbell

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    What do you informed folks term/describe as the below-mentioned?:-

    The measurement of the base of the case to the ogive of the bullet (whilst just touching) the lands of the rifling?

    The measurement from the base of the case to the ogive of the bullet?

    Many thanks in advance.
     
  2. Texas10

    Texas10 Gold $$ Contributor

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    CBTO = Cartridge Base To Ogive.
     
  3. Mulligan

    Mulligan Gold $$ Contributor

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    Touch, although how you arrive at “touch” is another conversation.
    CW
     
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  4. Richard Coody

    Richard Coody Gold $$ Contributor

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    just remember the ogive is a curve starting at the bearing surface of the bullet and going to the tip. CBOT is kind of an arbitrary measurement somewhere along that curve. unless you use the exact same tool your measurements will not match another reloaders.
     
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  5. retired

    retired

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    lets get busy
    OAL/COAL over all length/cartridge over all length
    cbto as above, is not likely a measurement to the lands
    "touching" as above and is user defined by how much land engagement you get
    at your version of "touch". i keep measuring till i can just barely see all lands
    touching the bullet. think polished bullet and a magnifying glass.
    some use "jam" "hard jam" but those terms lack definition.
    practice, learn what you consider touching.
    your tools and your throat are not likely to match anyone else's, so
    there is a learning curve to match what they said to what YOUR rifle likes
     
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  6. fguffey

    fguffey

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    And there is: I am the fan of the running start, I want my bullets to have that 'jump'.

    F. Guffey
     
  7. Campbell

    Campbell

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    It certainly is another conversation! Good Point!

    As I learn every day, nothing is as simple as I first thought.

    I think I will ask a separate question re how to determine an accurate measurement when just contacting the lands with the ogive of the bullet.
     
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  8. Mulligan

    Mulligan Gold $$ Contributor

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    Alex Wheeler @Alex Wheeler knows what he is doing.
    Enjoy
    CW
     
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  9. Campbell

    Campbell

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    Hi Texas10

    Many thanks for this!

    So, would "CBTO@L's" be an acceptable term to use where the measurement is where the bullet is just touching the lands?

    And, CBTO = Cartridge Base To Ogive.

    The reason I am asking all this is am designing a cartridge process check list that can be printed and included into the ammo box.

    Many thanks again.

    Cam
     
  10. Campbell

    Campbell

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    Hi M

    Many sincere thanks for this, I will digest later and get back to you!

    Cam
     
  11. barefooter56

    barefooter56

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  12. R.Morehouse

    R.Morehouse Gold $$ Contributor

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    And once you get it sorted out it will all be N.B.F.D.
    No
    Big
    Fu##ing
    Deal

    Sorry about that......o_O
     
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  13. Texas10

    Texas10 Gold $$ Contributor

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    CBTO-Touch, or any way you want to define it works, since this is something only YOU will refer to for your particular barrel. Anyone else's measurement is worthless to you, and your barrel will be eroding with use and the distance to lands will move forward as the throat erodes.

    I make a dummy cartridge for each caliber/bullet/barrel that is set to touch and keep it as a reference tool. I use it anytime I want to re-check distance to lands, and label it with date, CBTO dimension, bullet (lot, too if you wish) and anything else you think is important. Chart the erosion in your loading log.

    A very reliable way to check distance to lands and produce the above mentioned dummy cartridge is to take one of your fire formed and ready to load cartridge cases and drill and tap the flash hole for 6/32.

    Seat your bullet a bit long, screw it on a section of 3 piece cheap cleaning rod, and slide it up the pipe (bolt out of the gun) with a firm push. Then extract. If it tends to stick, it's in the lands. Reseat the bullet .010 deeper and repeat until you find the no-stick dimension. You can work this to down to .001 and you will actually feel the difference between touch and .001 off.

    You'll need to make sure your chamber is clean, and no carbon in the throat to get good, accurate, repeatable results.

    If you'd like pics of this process, shoot me a pm with your phone number and I'll text you.

    Good luck and keep the questions coming.
     
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  14. retired

    retired

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    your inventory of "dummy rounds" is good for what ? the throat moves when you shoot.

     
  15. dmoran

    dmoran Gold $$ Contributor

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    He said why. I do the same thing often enough. For reference is why I do it, just as @Texas10 said he does.
    Besides, you can re-use the case over and over for the task, if one chooses to.

    We all have our own ways of doing things, right? Good to hear others ways, no matter if we ever utilize them ourselves or not.
    Donovan
     
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  16. hogpatrol

    hogpatrol Gold $$ Contributor

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    New chamber, my m.o. is to take every bullet I am going to use, get a CBTO reference point for each one with both the Hornady tool and Alex's method, record the CBTO for each and put them away for future reference. Depending on the cartridge, after X amount of rounds, retrieve those bullets and re-check the CBTO. The key is to use the same exact bullets, not ones from a new box or lot.
     
    Last edited: Mar 13, 2018
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  17. hogpatrol

    hogpatrol Gold $$ Contributor

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    Where does it go? Does it return to it's previous state after the shot? Inquiring minds want to know.
     
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  18. retired

    retired

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    i do the same,,,to measure/track throat wear.
    but i load based on the current lot of bullets.
     
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  19. Mulligan

    Mulligan Gold $$ Contributor

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    ^^^^^yep, what he said. ^^^^^^^^^
    CW
     
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  20. Richard Coody

    Richard Coody Gold $$ Contributor

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    CBTO has nothing to do with touch. it can be any length. Now you can certainly use touch which is a very arbitrary measurement as your base to ogive length.

    define touch. could be anywhere from when you feel that first resistance when the bullet enters the throat, when the bullet actually touches the lands and leaves slight marks on the bullet or when the bullet actually engauges the lands. personally i like a full jam as my datum. where the bullet's forward movement stops. more repeatable for me. At any rate all this point is is a datum to start your seating depth test.
     
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