Bullet Bearing Surface Length Question(s)

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by royinidaho, Mar 8, 2009.

  1. royinidaho

    royinidaho Writers Guild

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    Anyone out there besides GG sort bullets by bearing surface length? (I've emailed GG)

    Some one on the 6BR site says sort them to 0.003"

    Would that be +/- 3 or an extreme spread of 3?

    Also, 0.003" seems a bit anal for a hunting situation vs BR shooting?

    Also, my bullets are coming out with the lighter bullets bearing surface lengths of 0.500
    The heavier bullets show a bearing surface length 0.0135" shorter than the lighter versions.

    Given the 12 grains difference in weight, what's the odds of getting the same velocity from both weight of bullets. Or in other words how much does bearing surface length affect pressure/velocity?

    Or should I even give a hoot??
     

  2. britz

    britz Well-Known Member

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    That's a good question. I just started doing it for the heck of it...but that doesn't mean that it's the right thing to do LOL :)
     

  3. AJ Peacock

    AJ Peacock Well-Known Member

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    Roy,

    I only sort my 338 bullets ( for my Edge and AM), these are my 2 "long range" rifles. Which bullets are you sorting? All the SMK's that I've sorted have not varied by weight at all. If I remember correctly, my extreme weight spread was .6gr for 1000 bullets and was caused by 2 bullets. The extreme spread of the rest was within .3gr.

    As far as length, I was sorting into .001" buckets with the SMK's. Not that it was necessary for accuracy (who knows?), but that's just how I sorted them.

    What bullets are you sorting? 12gr's seems like a pretty huge spread.

    As far as being anal as compared to the BR guys, I would guess that baring surface inconsistency has a larger affect on my 338AM at 1500yds than it does on a bench rester at 100yds.

    AJ
     
  4. royinidaho

    royinidaho Writers Guild

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    AJ

    I'm sorting Berger 7mm 168s and 180s (source of that 12 gr number) after I squeeze them down to 277.

    The bullets are pretty much +/- Zero for weight but vary a bit in overall length.

    Bearing surface varies a bit also.

    I know that vertical stringing @ LR will appear due to varying bearing surface length.

    What I was wondering is what's the odds of approaching the same velocity with both bullets with the 12gr heavier bullet's bearing surface being about 0.013 shorter?

    I guess I'll find out when I start shooting....
     
  5. davewilson

    davewilson Well-Known Member

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    generally speaking, what happens is the heavier bullet starts out a bit slower but has a little higher BC. this makes the trajectory very similar. i don't weigh sort my bullets but do separate by BS.
     
  6. royinidaho

    royinidaho Writers Guild

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    Dave,

    What's your sorting spec?
     
  7. davewilson

    davewilson Well-Known Member

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    groups of .002
     
  8. JeffVN

    JeffVN Well-Known Member

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    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
     
  9. Fiftydriver

    Fiftydriver <strong>Official LRH Sponsor</strong>

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    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.
     
  10. trueblue

    trueblue Well-Known Member

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    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 ?
     
  11. royinidaho

    royinidaho Writers Guild

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    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
     
  12. royinidaho

    royinidaho Writers Guild

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    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.
     
  13. Boss Hoss

    Boss Hoss Well-Known Member

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    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!
     
  14. uncleB

    uncleB Well-Known Member

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    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