G7 vs G1 what's the difference?

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by Ingwe, May 29, 2018.

  1. Ingwe

    Ingwe Well-Known Member

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    I was playing around with the JBS Program with 7mmRemMag 175gr Accubond LR bullets in mind, and it brought me to the question of, "What is the difference between G1 and G7?

    For example using said bullet at 3,000fps, I entered the BC value of .681 G1 and then the .326 G7 value, and I found that the difference between the 2 values at 1,000 yards is only 1 inch. Even at 1,500 yards it's only a 2 inch difference.

    Even Nosler states, "For the upmost accuracy, we recommend using the G7 value."

    From what I understand, G7 was created with boat-tails in mind and G1 for flat base bullets BUT for a difference of 2" at 1,500 yards I don't see how it means anything.

    Am I missing something here??
     
  2. Mike 338

    Mike 338 Well-Known Member

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    Not sure but did you check out wind drift?
     
  3. Ingwe

    Ingwe Well-Known Member

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    Still within an inch
     
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  4. Ingwe

    Ingwe Well-Known Member

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    That’s why I ended my post with “am I missing something?”

    I know that us shooters fret allot over little stuff but 1” at 1,000 yards is essentially nothing ....to me anyway

    Maybe someone else will chime in with an explanation on the issue
     
  5. Mike 338

    Mike 338 Well-Known Member

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    I suppose when your dealing with hit probability along with compound errors such as wind/range estimation, Coriolis, spin drift, shooter error, along with exterior ballistic modeling, maybe an inch would matter.
     
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  6. Mikecr

    Mikecr Well-Known Member

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    I agree with Mike 338. BC error contribute as many other errors do & it all adds up in complicated ways.
    The next time you're out, set up a 1/2moa target at 900yds, fire one shot at it.
    Then set up a 1/2moa target at 600yds, and fire one shot again.
    Then 300yds.
    Are you hitting all three?
     
  7. MudRunner2005

    MudRunner2005 Well-Known Member

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    They're 2 different measuring methods. G1 BC is calculable for any bullet (boat tail, flat base, etc...), but G7 BC is exclusively for boat-tail bullets, which will have both a G1 and G7 BC measurement.

    Straight from Berger's website...

    http://www.bergerbullets.com/wp_super_faq/what-is-the-difference-between-g1-and-g7-bc/

     
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  8. Ingwe

    Ingwe Well-Known Member

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    That sounds like allot allot of fancy lingo to explain a 1” difference at 1.000 yards;)
     
  9. Hatrick

    Hatrick Well-Known Member

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    Ing, When you shoot wich 1" is it. G1 or 7. I would shoot the one with the best match to my rifle. The least amount of variables in the mechanics the more of a mistake I can make.
     
  10. Timnterra

    Timnterra Well-Known Member

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    In theory the G1 and the G7 BC should land the projectile at the same place at 1000yds. However, this is a very complex mathematical equation. The introduction of the different BC profiles is just a means of making the calculations more true to reality. In a simple equation all you deal with is the trajectory but in reality there is a lot more going on. And to hit a target at extreme range you need everything in your theory to be as close to reality as possible. For some situations that means there is not much difference but you better believe everyone in the “king of two miles” was running G7 bc.
     
    Last edited: May 29, 2018
  11. Mikecr

    Mikecr Well-Known Member

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    Is this reality for you,, or purely theory?

    Either BC works at a single distance. Especially with fixed range target shooting.
    If the drag curve chosen is a bad match, it shows up as varying errors at multiple distances. That is, during hunting use.
    Such is often the case with today's low drag bullets -while assigned a G1 curve.

    A G7 curve may be a closer match. It could reduce some of the errors with multiple distance shooting. Measuring and entering actual air densities in ballistic software, adjusts the curve further to get more accurate. Minding your level matters. Entering the right scope height matters. Good MV data. Accounting for slope shooting. Latitude & bearing of shot matters at distance. Parallax,, consistent hold as tested,, ammo temps,, bullet stabilities, etc.
    It all matters, and it all adds up.
     
  12. Ingwe

    Ingwe Well-Known Member

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    Mike, obviously you know WAY more about the topic than I do;) but what I did was enter the exact same values on a JBM program and the only thing that I changed on the data was the G1 G7 value....when I did this I then compared the different drop in inches for G1 and G7....the result showed only an inch difference at 1,000 yards. So that was/is the purpose of my post. So with what I just wrote in mind, I still don't see much or really any difference between the two values if in the end it only amounts to an inch at 1,000 yards. It sounds like allot of technical mumbo-jumbo if in the end it only amounts to 1" at 1,000 yards.

    Mike BTW, how do you accurately measure your scope height? It's easy to find the center of the objective end of the scope but how do you measure the center of the bore to the center of the objective lense?

    Thanks!
     
  13. Mike 338

    Mike 338 Well-Known Member

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    Just measure the outside of your barrel just under the scope with some calipers and divide it by 2.
     
  14. Ingwe

    Ingwe Well-Known Member

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    And what about the space between top of barrel and bottom of objective ?