Posted: 2/14/2015 4:25:18 PM EDT
| Started loading Berger Classic Hunter 168 Grains for my .308. Probly a dumb question, but what is the G1 with BC of .496, and G7 with BC of .254 referring to? I understand BC , what is the G1 and G7? |
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Just different drag models. They say the G7 is better for long range boat tail bullets but I have used G1, and continue to, for my long range loads and they have always been on for me. Most I have ever been off is .2 mils at 1000 yards. That's about 7". Not too shabby.
Something to remember though with ballistics programs, "Garbage in, Garbage out" is very much in effect. Make sure you put in all the right data from bullet, environmentals, sight height etc. If not then the program won't help much. |
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Good link. Bottom line (TL:DR) is this:
The G1 model uses a flat-based projectile (think 125gr Hornady SST or Winchester 180gr Cor-lokt) as a perfect 1.000 The G7 model uses a boat tail projectile (think a 168/175gr SMK) as a perfect 1.000 This means the G7 is more accurate in modeling the velocity loss and wind deflection of modern long range rifle projectiles than the G7, and the most noted difference is in the trans-sonic and subsonic areas where the performance curves are very different (that is from Litz's book, not from the link). If you're not going into the trans sonic or subsonic region it shouldn't make much difference to you which you use. You can also successfully use programs that solve for G1 coefficients at differing velocities to get basically the same effect (if you can get this information). |
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Quoted:
Just different drag models. They say the G7 is better for long range boat tail bullets but I have used G1, and continue to, for my long range loads and they have always been on for me. Most I have ever been off is .2 mils at 1000 yards. That's about 7". Not too shabby. Something to remember though with ballistics programs, "Garbage in, Garbage out" is very much in effect. Make sure you put in all the right data from bullet, environmentals, sight height etc. If not then the program won't help much. That's odd. When I first tried using my app with my info I had it set to G1 and came up with 3.1 mils at 400yds. Wasn't anywhere around a 12" gong. Changed it to G7 and called for 2.5 mils. Dialed that in, and first round hit. And a hit everytime after that. |
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Quoted:
That's odd. When I first tried using my app with my info I had it set to G1 and came up with 3.1 mils at 400yds. Wasn't anywhere around a 12" gong. Changed it to G7 and called for 2.5 mils. Dialed that in, and first round hit. And a hit everytime after that. Quoted:
Quoted:
Just different drag models. They say the G7 is better for long range boat tail bullets but I have used G1, and continue to, for my long range loads and they have always been on for me. Most I have ever been off is .2 mils at 1000 yards. That's about 7". Not too shabby. Something to remember though with ballistics programs, "Garbage in, Garbage out" is very much in effect. Make sure you put in all the right data from bullet, environmentals, sight height etc. If not then the program won't help much. That's odd. When I first tried using my app with my info I had it set to G1 and came up with 3.1 mils at 400yds. Wasn't anywhere around a 12" gong. Changed it to G7 and called for 2.5 mils. Dialed that in, and first round hit. And a hit everytime after that. Did you use these BCs for the 175 gr SMKs? G1: .496 / G7: .243 |
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Quoted:
That's odd. When I first tried using my app with my info I had it set to G1 and came up with 3.1 mils at 400yds. Wasn't anywhere around a 12" gong. Changed it to G7 and called for 2.5 mils. Dialed that in, and first round hit. And a hit everytime after that. Quoted:
Quoted:
Just different drag models. They say the G7 is better for long range boat tail bullets but I have used G1, and continue to, for my long range loads and they have always been on for me. Most I have ever been off is .2 mils at 1000 yards. That's about 7". Not too shabby. Something to remember though with ballistics programs, "Garbage in, Garbage out" is very much in effect. Make sure you put in all the right data from bullet, environmentals, sight height etc. If not then the program won't help much. That's odd. When I first tried using my app with my info I had it set to G1 and came up with 3.1 mils at 400yds. Wasn't anywhere around a 12" gong. Changed it to G7 and called for 2.5 mils. Dialed that in, and first round hit. And a hit everytime after that. You put the wrong number in somewhere as my 400 yard load is 2.3 mils. Garbage in, garbage out. Make sure to use the right BC. |
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Quoted:
Just different drag models. They say the G7 is better for long range boat tail bullets but I have used G1, and continue to, for my long range loads and they have always been on for me. Most I have ever been off is .2 mils at 1000 yards. That's about 7". Not too shabby. Something to remember though with ballistics programs, "Garbage in, Garbage out" is very much in effect. Make sure you put in all the right data from bullet, environmentals, sight height etc. If not then the program won't help much. Why not just switch to using G7 models as they are clearly a better solution for what you are shooting? |
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Quoted:
Why not just switch to using G7 models as they are clearly a better solution for what you are shooting? Quoted:
Quoted:
Just different drag models. They say the G7 is better for long range boat tail bullets but I have used G1, and continue to, for my long range loads and they have always been on for me. Most I have ever been off is .2 mils at 1000 yards. That's about 7". Not too shabby. Something to remember though with ballistics programs, "Garbage in, Garbage out" is very much in effect. Make sure you put in all the right data from bullet, environmentals, sight height etc. If not then the program won't help much. Why not just switch to using G7 models as they are clearly a better solution for what you are shooting? Because I know what I am using works. I stick with things that are tried and tested by me and work for me. Same with gear. I am fine with trying new things but I won't abandon something that works for the latest thing the internet says I have to use. I have used G1s out to 1650 yards with my 300WM and hit. They work. People read things that say they don't and then all of a sudden they don't work anymore? Nope they work just fine. |
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Quoted:
Because I know what I am using works. I stick with things that are tried and tested by me and work for me. Same with gear. I am fine with trying new things but I won't abandon something that works for the latest thing the internet says I have to use. I have used G1s out to 1650 yards with my 300WM and hit. They work. People read things that say they don't and then all of a sudden they don't work anymore? Nope they work just fine. Quoted:
Quoted:
Quoted:
Just different drag models. They say the G7 is better for long range boat tail bullets but I have used G1, and continue to, for my long range loads and they have always been on for me. Most I have ever been off is .2 mils at 1000 yards. That's about 7". Not too shabby. Something to remember though with ballistics programs, "Garbage in, Garbage out" is very much in effect. Make sure you put in all the right data from bullet, environmentals, sight height etc. If not then the program won't help much. Why not just switch to using G7 models as they are clearly a better solution for what you are shooting? Because I know what I am using works. I stick with things that are tried and tested by me and work for me. Same with gear. I am fine with trying new things but I won't abandon something that works for the latest thing the internet says I have to use. I have used G1s out to 1650 yards with my 300WM and hit. They work. People read things that say they don't and then all of a sudden they don't work anymore? Nope they work just fine. Not saying you can't make it work, just that the G7 model is much closer to the actual bullets you are shooting. |
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Quoted:
You put the wrong number in somewhere as my 400 yard load is 2.3 mils. Garbage in, garbage out. Make sure to use the right BC. Quoted:
Quoted:
Quoted:
Just different drag models. They say the G7 is better for long range boat tail bullets but I have used G1, and continue to, for my long range loads and they have always been on for me. Most I have ever been off is .2 mils at 1000 yards. That's about 7". Not too shabby. Something to remember though with ballistics programs, "Garbage in, Garbage out" is very much in effect. Make sure you put in all the right data from bullet, environmentals, sight height etc. If not then the program won't help much. That's odd. When I first tried using my app with my info I had it set to G1 and came up with 3.1 mils at 400yds. Wasn't anywhere around a 12" gong. Changed it to G7 and called for 2.5 mils. Dialed that in, and first round hit. And a hit everytime after that. You put the wrong number in somewhere as my 400 yard load is 2.3 mils. Garbage in, garbage out. Make sure to use the right BC. You're right. I didn't realize you have to change the BC when going between drag models. I still had .247 in when I changed it to G1. I put in .496 and it got me closer. Called for 2.2 mils instead of 3.1 lol. But the G7 calls for 2.5 and works so far. I'll keep with the G7 for me. |
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Quoted:
Just different drag models. They say the G7 is better for long range boat tail bullets but I have used G1, and continue to, for my long range loads and they have always been on for me. Most I have ever been off is .2 mils at 1000 yards. That's about 7". Not too shabby. Something to remember though with ballistics programs, "Garbage in, Garbage out" is very much in effect. Make sure you put in all the right data from bullet, environmentals, sight height etc. If not then the program won't help much. Same here... |
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Quoted:
Started loading Berger Classic Hunter 168 Grains for my .308. Probly a dumb question, but what is the G1 with BC of .496, and G7 with BC of .254 referring to? I understand BC , what is the G1 and G7? I am not shooting that particular bullet, but I just picked up Bergers reloading manual and I noticed that on virtually every load data page they explicitly recommend use of G7 and provide G7 BC. I suspect they know what works best with their bullets. |
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guys, the difference in experiences here is not easily explained, but is due to the fact that the various ballistic calculators use different underlying formulas. those formulas all need a 'constant' that represents the resistance of air on the bullet, but they don't all use it the same way because they are not all based on the classic drag models.
some well respected ballistic calculators, like field firing solutions, only use "G1" but it's really just a number and you have to calculate it yourself using tools that come with the program. Others like litz/pejsa prefer G7. this article may help http://en.wikipedia.org/wiki/Ballistic_coefficient#The_G_Model my advice would be to use the one recommended by whomever wrote your ballistic calculator. the differences in experience are also partially explained by different expectations about how close a calculator is supposed to be. i.e. how large the target is |
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Guys,
In Bryan Litz's book APPLIED BALLISTICS FOR LONG-RANGE SHOOTING chapter 2 "The Ballistic Coefficient " explains what the G1 and G7 are based on and gives added information on "form factors' and such that affect the bullets BC. Very good read with lots of information. Also in the FAQ drop down under the INFORMATION tab on the main page is a shorter explanation. Hope this helps! Take care, Phil Hoham Berger Bullet Tech |