G1... G7... ??

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by Mike6158, Dec 8, 2009.

  1. Mike6158

    Mike6158 Well-Known Member

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    I have been using LoadBase (cool program but way over my head in many places. I plan to fix that.) and I just received a couple of boxes of Berger 168 gr. VLD hunting bullets (7 mag were back ordered). I also use a little iPhone app for ballistics as well as LoadBase on a pocket PC (best way to go imho). All of them have references and data entry points for G1 - G7, etc

    For instance:

    The bullet box says:

    G1 BC = .473
    G7 BC = .242

    BC I understand... G1 and G7 I'm not so sure. I assume that it's related to muzzle velocity and some other velocity downrange. Since this appears to be a standardized measurement I'm guessing it's yardage (or meters)? Not velocity though for each load there will be an equivalent velocity for an equivalent point in the trajectory.

    Just curious...
     
  2. RockyMtnMT

    RockyMtnMT Official LRH Sponsor

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    They are two different drag profiles. The G7 is a more accurate profile for the bullets that we are using. The G1 is older technology. Looks better, but not as accurate. If you have G7 #'s, use them.

    Steve
     

  3. BryanLitz

    BryanLitz <b>Official LRH Sponsor</b>

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    Mike,
    Please read this article.
    It explains the difference between BC's referenced to the G1 and G7 standard.
    If you have any further questions about referencing BC after reading that, please post back and we can help. That article should give you the main idea.
    -Bryan
     
  4. bigngreen

    bigngreen Well-Known Member

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    The LoadBase manual is real good also, I've been using the new Berger G7 numbers and they have been right on, no tweeking as long as you remember to toggle to G7.
    I'm going to get Brians book, I'm thinking it may straighten things up in my brain also.
     
  5. RockyMtnMT

    RockyMtnMT Official LRH Sponsor

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    That will explain it much better than I.

    Steve
     
  6. Kevin Thomas

    Kevin Thomas Well-Known Member

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    Rocky,
    a slight correction here; the G1 is no older than the G7. They were developed at the same time and by the same guy, E.D. Lowry of Winchester/Olin. The G1 has been the default drag model that has been in use ever since as sort of a compromise standard for everything, including more modern design bullets that don't accurately match the resulting trajectory shown by that model. Berger's trying to change that, and educate the current generation to use the proper drag model, and enjoy the benefits of a truly accurate trajectory prediction.

    I'm sure Bryan's link explains a ll this in his usual detail! :)

    A little history . . .

    Kevin Thomas
    Lapua USA
     
  7. RockyMtnMT

    RockyMtnMT Official LRH Sponsor

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    Thanks Kevin. I think I Knew that but had forgotten, rings a bell anyway. G7 seems new.:rolleyes:

    Steve
     
  8. Kevin Thomas

    Kevin Thomas Well-Known Member

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    Hey Steve,

    It DOES seem that way, all courtesy of Bryan. If not for his efforts and the push by Berger, you still probably wouldn't be hearing much buzz about it (the G7). Bryan's an engineer and thus a pragmatist, and just wants to see the correct drag model used that's appropriate to the bullet being used, and I applaud him/them for that. The result, of course is better downrange trajectory tables and enhanced hit potential for the shooter.

    On the other hand, I'm a historian, and just enjoy tilting at windmills. I would like to see folks get a better understanding of what all those different tables and drag models are used for, and a bit o the story behind them. What can I say? We all have our hobbies! :)

    Kevin Thomas
    Lapua USA
     
  9. Jeff In TX

    Jeff In TX Well-Known Member

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    Good thread folks. When it comes to bullet designs, Bryan and I and few others on some other shooting boards have been trying to help folks understand why a G1 BC is obsolete, actually has been since it’s inception but proved to be a great marketing tool for bullet companies. The G7 BC has become the new focal point primarily because of Bryan’s work at Berger.

    Berger designs and builds some of the best VLD shooting and hunting bullets on the market and with Bryan’s knowledge, field testing and resources he’s posted a vast library of G7 coefficient drag model BC’s. This has been a huge win win for the shooting public and it’s finally making other bullet manufactures take notice that the old G1 BC isn’t going to cut it much longer. Shooters are becoming educated to the real facts of BC’s!

    Having said that, not every type of bullet will fit the G7 coefficient drag model either. The G7 coefficient drag model was developed for VLD bullets and that’s Berger’s bread and butter bullets, it's what they know and do very well!

    A lot of boat tail bullets such as Sierra’s BTHP Match king bullets better fit the G5 coefficient drag model rather that the G7. Flat base spire points use a G6 coefficient drag model. However, mathematically we may be splitting hairs with some boat tail bullets and you’ll always be much better off using a G7 coefficient drag model than a G1.

    My point is, there are a number of different coefficient drag models to choose from for different bullet designs. Using the proper coefficient drag model for the type of bullet you’re shooting will always produce the best results when using a ballistic program.

    And Bryan, thanks for all your research and testing, you’re still the man!
     
    Last edited: Dec 9, 2009
  10. MontanaRifleman

    MontanaRifleman Well-Known Member

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    Jeff, which drag model would fit Nosler E-Tips the best?

    Mark
     
  11. Mike6158

    Mike6158 Well-Known Member

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    Wow... Awesome responses... Guess what came in the mail today?

    Applied Ballistics for Long Range Shooting by Bryan Litz :D

    I'll read the article too. I really appreciate the responses!
     
  12. ROBSTER

    ROBSTER Well-Known Member

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    That helps me also but i have rsi shooting lab and there is a listing for g8 is that a newer profile than g7?
     
  13. Jeff In TX

    Jeff In TX Well-Known Member

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    Robster, the G8 is for a flat base VLD not a boat tail VLD bullet.

    Mark,

    Dang you I knew sooner or later someone would ask that question and open a whole new can of worms. The long and short of it, each bullet needs to be measured and tested to see what coefficient drag model it fits into. There’s not a one size fits all and the hope is bullet manufactures would step and provide this information for the shooter.

    Berger has essentially started this with Bryan publishing the G7 BC’s for their bullets as well as many other bullets. But as I stated Berger’s bread and butter bullets are their VLD bullets so they fall nicely into the G7 coefficient drag model.

    We’ll not likely get this support or information out of Sierra any time soon. They like the higher BC’s of the G1 drag model…”marketing tool”! Also their ballistic program massages the G1 calculations by using multiple G1 BC’s across different velocities to get more accurate results. IMHO this is poor idea and just a band-aid trying to get an obsolete G1 drag model to more accurately predict bullet flight using their ballistic program. The real issue is how you accurately measure the multiple BC’s over those different velocities? Also the G1 BC can change gun to gun (barrel to barrel) depending on bore diameter, twist rate and barrel length. So it’s a crap shoot at best.

    I use the RSI Ballistic Lab program and it has a drag modeling tool for determining the correct drag model. It works really well for me. I spend a lot of time working ballistic calculations. I also spend a lot of time tweaking my ballistic program inputs. I can get my ballistic program to match my actual shooting data very accurately. In the end it comes down to the data you input into your ballistic program that determines the output data. Understanding how everything works together and what inputs conflict with other inputs can determine just how accurate your results can be.
     
    Last edited: Dec 9, 2009
  14. Kevin Thomas

    Kevin Thomas Well-Known Member

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    Jeff,
    A quick defense of the use of the G1 in the older programs here, or at least a bit of background. The guys who do the Sierra ballistics portion of the manuals and software have been with the company as contract employees for over thirty years now; Bill McDonald and Ted Almgren. They are not, however, and never have been Sierra "employees." Both are very dear friends of mine, and guys for whom I have tremendous respect. Their association with Sierra resulted from their walking in to the front counter (literally) to buy some factory seconds back in the 70s, while we were all still in Santa Fe Springs, CA. At that time, Sierra was still "calculating" their BCs via the Coxe-Bugeless tables. No time of flight firings, no radar, no nothing. Bill and Ted struck up a conversation with Ken Smith (then the plant engineer) and/or Bob Hayden and explained a bit about what they could do to determine true BCs for the bullets by actually measuring the time of flight results. This, in turn lead to their long association with the company, and a progressive string of ballistic software over the years. And, I might add, some of the first true time of flight measured BCs within the bullet industry. They're still involved, though long since retired from their "day jobs." At the time they initially offered their services, you have to understand that very few folks outside of professional ballistic labs had ever so much as HEARD of Ballistic Coefficient, much less knew anything about how it worked. The only BCs being used by even major bullet and ammunition manufacturers at that time were tied to the G1, simply to keep everything at a "manageable" level of understanding. Bill and Ted realized that there were inherent limitations in using the G1 for everything (as it was the industry practice to do at that time), and set about trying to do something to deliver more accurate downrange data in the programs. The multiple velocity BC break points was Bill's solution, and he'd be the first to tell you that it is at best an imperfect fix. It was, however, the best they could do at that time, and still remain in the same pond with all the other ducks, such as Speer, Hornady and Nosler. Over the last few decades (largely due to AlGore's invention of the internet :D) the shooting community has become tremendously better educated. Look no further than these boards, or this very thread for proof of that! It was only about twenty years ago that I read in print, from a VERY well known gunwriter, that BC was time of flight in a vacuum compared to time of flight in atmosphere. A comment like that today would likely get one laughed off these boards, permanently. Yeah, we've come a long way since then. Berger as a corporate entity, and Bryan in particular, have been the ones who've really stepped up to the plate and pushed this issue to the forefront. With the incredible variety of software out today, I think the situation is quite a bit different than when Ted and Bill offered the shooting public an initial peek into the unseen world of Ballistic Coefficients and trajectory calculations. Prior to them, the only people who had a clue about most of this were folks who'd waded through the classic Hatcher's Notebook or the other very complex texts relating to exterior ballistics. Few and far between, I assure you. While I hear the old saw that the other companies hold to the G1 drag model due to the higher numbers associated with them (and hence, sales appeal) I can pretty well assure you that's not the case. For many today, it's simply "status quo" and as we all know, inertia can be hard to overcome. Anyway, cut 'em some slack (Bill and Ted, anyway) and give credit where credit's due. If we have a better view of the world today, it's because we're standing on their shoulders.

    Kevin Thomas
    Lapua USA