Bearing Surface Length Measurement Question

Discussion in 'Reloading' started by royinidaho, Dec 14, 2006.

  1. royinidaho

    royinidaho Writers Guild

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    I rigged up the following gizmo which as passed all of my tests for usefulness and consistency of measurement.

    My question is what should the diameter of the hole be to provide data that is consistent when shared with others. Info to be shared would be Base to Ogive, bearing surface length.

    I guess that there must be a pretty much standard ogive diameter??? I read somewhere to make the hole 0.011" under the cal. diameter. Not sure if that's a good number.

    Cals I'm interested in are 222, 277, 338.

    Any help would be appreciated. Thanks

    [​IMG]
     
  2. jmden

    jmden Well-Known Member

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  3. royinidaho

    royinidaho Writers Guild

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    Where in the heck have I been /ubbthreads/images/graemlins/blush.gif

    Its ordered.......

    Thanks
     
  4. davewilson

    davewilson Well-Known Member

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    most comparators use something close to the bore dia of the caliber. a 308 would be .300... a 270 would be .270. i think a 224 would be .218, not sure about that one. a 338 would be .330.
     
  5. royinidaho

    royinidaho Writers Guild

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    Dave, If I had half a brain I would have known that! Duh!

    Nevertheless the Sinclair thinger is on the way.

    When are we gonna get further info on your project......
     
  6. goodgrouper

    goodgrouper Well-Known Member

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    The Stoney point method works just as well and is cheaper. You could possibly even make a way to hook the inserts up to your contraption if you got inventive enough.
     
  7. royinidaho

    royinidaho Writers Guild

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    Grouper, I'm getting tired of all of this innovativeness /ubbthreads/images/graemlins/blush.gif I've had that bad habit so long I have no idea of where I got it.....

    The sinclair thinger will go under the dial indicator. I'll just have to set it up an inch or so higher on the rod.

    + Santa's gonna bring me a digital caliper. I can never find my magnifying glass for the one I've had for 30 years. /ubbthreads/images/graemlins/frown.gif /ubbthreads/images/graemlins/frown.gif
     
  8. Mikecr

    Mikecr Well-Known Member

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    This is the best I've used:
    http://www.davidtubb.com/tcom_images/reloading/bsc_one.html

    The Sinclair thingy is handy as heck for OAL/seating depth checks, but won't help with bearing surface measurements. Nor will the Stoney point rigs(which I hate).

    Bearing surface doesn't start anywhere near bore diameter. It starts at caliber, both at the nose and boat tail.
     
  9. davewilson

    davewilson Well-Known Member

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    Mike, we understand that the ogive starts at complete bullet dia. the question was what dia hole should be used to check bearing surface length.most use something around the bore dia. for this operation. if you read the info on the one you like, it also uses bushings with holes that are "bore diameter"

    Roy, i'd like to post some pixs of my project as there are several that would like to see it. my problem with this is i can't get my computer enlightened stepsons over hear to take pictures and of course, post them for me.i also have heard from many that i have fractional brain loss except they usually use a fraction that is much greater than 1/2! hoping to get-r-done this weekend.
     
  10. BountyHunter

    BountyHunter Writers Guild

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    The Buhay Ogive checker is the top of the line. It looks exactly like the Tubbs because John Buhay makes it and sells it to David. It is also sold thru RW Hart and sons in PA for $125. It is more accurate than the stoney points due to variance in pressure for most people. If you are a machinest and have calibrated hands the stoney points work well.

    BH
     
  11. royinidaho

    royinidaho Writers Guild

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    [ QUOTE ]
    Bearing surface doesn't start anywhere near bore diameter. It starts at caliber, both at the nose and boat tail.

    [/ QUOTE ]

    Now I'm really confused. I drill my holes @ 0.277 and 0.338 and guess what? Just as common sense (which I am a bit short on these days /ubbthreads/images/graemlins/blush.gif) would indicate the bullets very precisely slid through. At that moment the ol' noggin kicked in. Thus the above question.

    My objective would be to measure Base to Ogive (or whatever that standard diameter ends up being) and sending the round to say Dave, for example, and he measures the same within reason.

    Further, when I "cram" a seated bullet into the rifling to determine max length, and am lucky enough to not have the bullet stick in the barrel or be too loose in the neck and slide a bit, on factory rifles the bullet is marked with rifling marks. I back off on the seating die until there are no marks and define that length as COL.
     
  12. goodgrouper

    goodgrouper Well-Known Member

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    [ QUOTE ]
    The Sinclair thingy is handy as heck for OAL/seating depth checks, but won't help with bearing surface measurements. Nor will the Stoney point rigs(which I hate).


    [/ QUOTE ]

    Yes they will. Two Stoney Points measure the same thing the Tubb's do. And in fact, when measuring several hundred 300 grain MK's with both the Tubb's and the Stoney POints, all but just a very few measured into the same piles of segregation. The ones that differed were only a .001 or two. Tubb's is certainly more refined, but either method accomplishes the job just as well. Constant pressure on the SP is fairly easy to attain with some practice.
     
  13. jmden

    jmden Well-Known Member

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    Roy, I hope I didn't steer you wrong with the Sinclair Comparator. I looked at your picture and saw what you were measuring and thought 'why not the Sinclair gizmo'? But, it look like you are trying to measure bearing surface, which the Sinclair Bullet Comparator isn't specifically designed for.
     
  14. davewilson

    davewilson Well-Known Member

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    Roy, i gave you the hole sizes you need to drill?

    these comparators don't actually give you the bearing surface length. they simply give you a method of segregating bullets so they all have similar bearing surface length.