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Ballistic Coeficient G1 or G7

 
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  #1  
Old 05-01-2012, 04:19 PM
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Ballistic Coeficient G1 or G7

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?
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  #2  
Old 05-01-2012, 06:01 PM
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Re: Ballistic Coeficient G1 or G7

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
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Old 05-01-2012, 09:24 PM
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Re: Ballistic Coeficient G1 or G7

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.
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Old 05-02-2012, 05:48 AM
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Re: Ballistic Coeficient G1 or G7

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.
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Old 05-02-2012, 05:58 AM
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Re: Ballistic Coeficient G1 or G7

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??
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Old 05-02-2012, 08:15 AM
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Re: Ballistic Coeficient G1 or G7

Quote:
Originally Posted by scsims View Post
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??
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
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Old 05-03-2012, 06:43 AM
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Re: Ballistic Coeficient G1 or G7

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