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.
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.
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Bearing surface doesn't start anywhere near bore diameter. It starts at caliber, both at the nose and boat tail.
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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 [img]/ubbthreads/images/graemlins/blush.gif[/img]) 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.
I may be the slowest guy on the mountain . . . . but . . . . I'm on the mountain!
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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).
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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.
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.
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