bullet bearing surface ?

[Gman]

I've searched, and can't find the article that showed the 'measured bearing surface' of various 6 mm. bullets. I am mainly concerned with the 95 gr. to 108 gr. projectiles. Is it fair to say that, if 2 Brands of bullets weigh the same amount of grains, but Brand A's bearing surface is GREATER than Brand B's bearing surface, then Brand A will have higher internal pressures,in the chamber/bore) than Brand B, if the fired rounds were made up of the exact same brass, primer, and weight charge of powder, and fired through the same rifle.

 

[Preacher]

You have that figured out just right.....

 

[Gman]

Preacher, do you remember the write-up,,on this site), in which one of the forum members documented the measured bearing surface of quite a few 6 mm bullets ?

 

[Preacher]

No sir I don't... They all vary enough that I would want to do my own measuring anyways..

 

[jb1000br]

Guessing this is it:

http://accurateshooter.wordpress.com/2008/08/16/6mm-bullet-diameters-update/

German Salazar did bearing surfaces, OAL and diameters, and I measured diameters.

JB

 

[Gman]

Thank You, JB. That is what I was looking for !

 

[TonyR]

The variation of bearing surface within a box or boxes of the same lot of bullets is also interesting. I measured 500 Berger 6mm 105 VLDs and found a .012 inches difference between the longest and shortest bearing surface. I just did the same thing with 500 7mm 180 VLDs and the maximum difference was .014 inches. In both cases, most of them were within .008, but I think it is worth sorting them.

 

[jb1000br]

Tony, what tool are you measuring with?

My 3 year old lot of Berger 105 VLD's only varies +-0.002' with most being +-0.001'

Surprised to hear your numbers.

JB

 

[TonyR]

I was surprised the first time I did as well. I use two Sinclair Comparators back-to-back on a pair of dial calipers. I have thought about trying to find one of the Buhay gadjets, but this seems to work fine. The measurement will sometimes vary by .001 or so when I re-measure a couple but I believe that I am pretty close on the extreme spread. I also found a statistically significant velocity difference with variation in bearing surface in a test I did last year to see if sorting is worthwhile. I'll post a table of the number of bullets in each size for the 7mm 180 VLDs I just measured if you think people would be interested. I didn't keep the data for the 105s and most of them are gone now.

 

[jb1000br]

Weird...

I use 2 stoney points on calipers as well...might want to get with Eric Stecker on those...I GUARANTEE he will be interested to see them.

Take care,
JB