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Bullet Bearing Surface Length Question(s)

 
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  #8  
Old 03-11-2009, 08:26 AM
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Re: Bullet Bearing Surface Length Question(s)

I sort by bearing surface, not weight. The increments depend upon the particular bullets that I'm sorting. My 7mm Berger 180s, I go 0.001, my 338 300 Grain SMKs I go 0.002.

JeffVN
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  #9  
Old 03-11-2009, 09:49 PM
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Re: Bullet Bearing Surface Length Question(s)

I sort by +/-0.001 thou. Once you find the mean of the lot of bullets you have, if they are good quality, most often 80-90% of them will fall within this range. The reason I will reserve for fouling shots.

I have found it interesting that the more extreme a chambering is, the more baring surface will show up down range. WHen I was shooting the 200 gr ULD RBBT Wildcat bullet in my 7mm AM loaded to just under 3300 fps.

At 500 yards, there was no real difference in impact no matter what the baring surface variation was, within reason.

At 1/2 mile you could start to see the effects of it if bullets were not sorted by BSL. At 1000 yards, you could cut groups by 1/2 moa by shooting sorted bullets. At 1500 yards, it could be easily 1 moa veritical stringing.

That said, in a 270 Allen Xpress(300 Dakota) and the 169.5 gr ULD RBBT, there was not nearly as noticable stringing, even with same BSL variation........

This brings me to the following conclusions:

A. The shorter the baring surface length, the less effect this variation will have down range.

B. The lower the expansion ratio of a given cartridge, the more baring surface variation will effect down range stringing.

Now this certainly may not be the case in every situation but its repeated itself enough to make me believe it.

Simply put, sorting by BSL is easy to do, why not do it just because.
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  #10  
Old 03-11-2009, 09:57 PM
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Re: Bullet Bearing Surface Length Question(s)

I have been following this thread, and have a question. What are you guys using to sort bearing surface length ? Something from Sinclair, with dial indicator ?
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  #11  
Old 03-11-2009, 11:36 PM
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Re: Bullet Bearing Surface Length Question(s)

Quote:
Originally Posted by trueblue View Post
I have been following this thread, and have a question. What are you guys using to sort bearing surface length ? Something from Sinclair, with dial indicator ?
GG uses two bullet comparators, one for each jaw of a dial caliper. He says its as accurate and faster than some of the higher prices units.

Here's a link to the Stoney Point which seems popular. Hornady makes one also.

I guess you just get two of the little red thingers and the proper caliber inserts and you're in business.

Stoney Point Bullet Comparator B-2000
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  #12  
Old 03-11-2009, 11:39 PM
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Re: Bullet Bearing Surface Length Question(s)

Kirby,

That's good first hand information.

For some strange reason the BLS on the 180s are coming out shorter than the 168s

Some one otta check BSLs of Berger 168s vs 180s in 7mm and see if things are consistent.
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  #13  
Old 03-12-2009, 02:01 AM
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Re: Bullet Bearing Surface Length Question(s)

John Buhay makes the "gold standard" of this type of measuring device. David Tubbs sells them under his name I believe. Personally I would not part with mine!
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  #14  
Old 03-12-2009, 09:36 AM
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Re: Bullet Bearing Surface Length Question(s)

I have both the Buhay unit and the two stoney point set-up. they both have their advantages.
The two stoney point OAL checkers on a dial caliper is way faster and way less expensive, the downside is that if you think you are sorting by .001" you are kidding yourself. in reality it might be as good as .002"-.003"
The Buhay unit is slower and much more expensive but is capable of sorting to .001"
In most cases .002"-.003" is good enough and the stoney point set-up is a good place to start you can up-grade later if needed.
UB
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