Ballistic Coeficient G1 or G7

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by scsims, May 1, 2012.

  1. scsims

    scsims Well-Known Member

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    I just downloaded the Shooter program for my phone and didn't know if I should use the G1 or G7 BC. I'm shooting a .308 168gr SMK. The G7 seems closer to what I've seen in the field shooting, G1 seems to be about 1.5 MOA off.

    How do I know which to use?
     
  2. Broz

    Broz Well-Known Member

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    The G7 is usually closer at the longer distances. I feel either will work for your 308 if you have solid velocity input along with accurate field conditions. Watch shooting too close to the chronograph. I keep em 18' from the muzzle so the blast does not interfear. Also remember many cheaper chrono's will lie. I would use the G7 and check the drops at 300, 500, 700 and 1000 on the same day and range if possible. Then use the velocity that puts them all spot on to .25 moa average from center group.

    Jeff
     

  3. kc0pph

    kc0pph Well-Known Member

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    G7. I dont want to take business away from Eric over at Berger Bullets, but he has a book with an entire chapter explaining what i am about to cover.

    If your bullet looks like a Flat Base say 55gn V-Max bullet (.22) you should use G1.
    If your bullet has a Boat Tail then use G7.

    The G1 is not Bad it just does not model a Long range Projectile as closely as the g7. I believe a 6mm Lapua Scenar bullet is a close resemblence to the G7 Standard Projectile.

    I would highly reccomend picking up his book. Costs $50 and is worth ever penny. HUGE hard cover book filled with information. If it was a college text book it would be $400... That is how nice it is.
     
  4. Greyfox

    Greyfox Well-Known Member

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    I have experienced no difference between the two using my 6.5x284 with 140 VLDs out to 1000 yards. My ballistic calculator shows about a 1-2" difference in elevation at 900 yards and this appears consistent with actual impact points. I haven't tested past 1000 yards, but my calculator begins to show more significant differences, with less correction using G7. The ballistic curves in Bryan's book appears to bear this out as well.
     
  5. scsims

    scsims Well-Known Member

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    Now that I have all the correct info in the program, it looks like G7 has 9.4 MOA @ 500 and G1 has 11.2 MOA.

    So actually G1 is closer to what I'm seeing. I guess I just use which is closer and adjust my MV to make the program match field results??
     
  6. Broz

    Broz Well-Known Member

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    There is no way they should be that different. You have something else wrong in one of those bullet models.

    At 500 yards you should see a very small or no difference at all.

    I suggest you go over your input data , you have something throwing one off.

    Jeff
     
  7. Mikecr

    Mikecr Well-Known Member

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    Hopefully your not using a G1 BC with the program setting at G7.
    G7 BC should lower than G1 BC.
     
  8. kc0pph

    kc0pph Well-Known Member

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    I find it hard to believe after reading most of his book that with a boat tail bullet you will get more consistent results with G1. I would be willing to bet that you are not inputting the correct items.

    If you think about it, use the model that looks like your bullet, G1 looks like a Pistol FMJ bullet, whereas the G7 looks like a Lapua Scenar.

    Check your inputs.
     
  9. scsims

    scsims Well-Known Member

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    I'm using 168gr SMKs .308 BC of .462 and Nosler BT 165gr BC of .490. So what would the G7 BC be?
     
  10. kc0pph

    kc0pph Well-Known Member

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    according to bryan litz
    168 smk g7 is .218 g1 is .427


    the nosler 165 balistic tip
    g7 .227
    g1 .444

    use the G7 that i have given you, they were tested by Mr. Litz himself rather than computer generated.

    Those were Average BC's from 1500 - 3000 fps i believe. That will get you VERY close on almost ANY shooting situation. If you need more precision id reccomend buying his book and it has all that information in it.


    I feel bad giving any more information that that, as the guy worked hard on the book and provides it for dirt cheap.
     
  11. Greyfox

    Greyfox Well-Known Member

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    Brian states in his book that the 168SMK has an inherent stability issue at ranges greater than 700 yards or so. It is a design flaw with of the bullet. Also, the Ballistic tip, due to the short boat tail, may behave more like a G1 then a G7. I use this 165gr. bullet in my 308 at 2800 fps and get very accurate trajectory results using G1.
     
  12. kc0pph

    kc0pph Well-Known Member

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    Just to clarify above I have never shot either of these bullets, and maybe have shot 5 30 cal rounds in my life :)

    Just took it from the book, shout of said above that i have no experience with either of these bullets (or the caliber for a matter of fact :p)
     
  13. timmyatnop

    timmyatnop Well-Known Member

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    My brother just bought a kestrel 4500 with a trac .. it just uses a g1 bc .. no input for a g7.. spot on at 550yards and 750 but i had to adjust my fps a littel bit.
     
  14. huntin_fool

    huntin_fool Well-Known Member

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    I was wondering the same thing. I was playing with shooter on my phone and with data for my 338 edge, using the g1 it says come up 25.1 and the g7 says 21.1. Any help?