I've been doing so research on the internet and can't seem to figure out which BC to use. My 190gr Bergers say G1 .291 and G7 .570 on the box. Which one should I use? Wiki says G1 is flat based "old style" bullets while G& are boattail streamlined bullets. How can these Bergers change shape, or why do they give you 2 different G factors?
BC factors, G1,2,3...?
- Thread starter shakeyjake
- Start date
I would suggest buying Applied Ballistics for Long Range Shooting. It is a great reference book and a wealth of knowledge. I would personally use the G7 numbers due to the fact that the bullet the G7 model is based on will more closely match the bullet you are currently shooting. This in turn will result in more accurate corrections when you use a ballistic program.
Scharfschütze
Regular
- Location
- Courtenay B.C.
Use G7 it is more accurate than G1 and G5. JBM dose have G7 listed for most bullets (I know they do for the .308 175gr SMK) It will list it as Berger, .308 cal, 190gr VLD (Litz) Litz refers to Brian Litz who wrote a book about ballistics. Here is the website I am talking about http://www.jbmballistics.com/cgi-bin/jbmtraj-5.1.cgi
Thanks, searching for the book now.
http://www.gun-blog.com/2013/02/what-is-g1-and-g7.html
What is G1 And G7?
G1 tells you how bullets shaped like this slow down in air:
For the typical hunting bullet both are a bit off, but inside 300 yards it doesn't matter much.
Sierra use radar to calculate multiple BC vales to fix this problem, if you have a suitable app.
What is G1 And G7?
G1 tells you how bullets shaped like this slow down in air:
http://3.bp.########.com/-pAQQ0KMvlJw/UR1NMkwkPYI/AAAAAAAAAVw/Uxk84iCzIQM/s320/G1.png
G7 tells you how bullets shaped like this slow down in air:http://2.bp.########.com/-sE_pCweHrQo/UR1NM6BmWbI/AAAAAAAAAV0/TrnKdNfj6zY/s320/G7.png
So G1 isn't great for real bullets, and G7 is great for pointy long-range boattails.
For the typical hunting bullet both are a bit off, but inside 300 yards it doesn't matter much.
Sierra use radar to calculate multiple BC vales to fix this problem, if you have a suitable app.
I like the G1 for the simple reason that it works well for comparison purposes.
What I mean is that if you were to fire 2 bullets at the same muzzle velocity and one had a G1 BC of .200 and the other a G1 BC of .500 the downrange velocity of the .500 BC bullet at 500 yards would equal the 200 yard velocity of the .200 BC bullet…. Same for wind drift.
Cool huh?
What I mean is that if you were to fire 2 bullets at the same muzzle velocity and one had a G1 BC of .200 and the other a G1 BC of .500 the downrange velocity of the .500 BC bullet at 500 yards would equal the 200 yard velocity of the .200 BC bullet…. Same for wind drift.
Cool huh?
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You have your numbers mixed up. G7 is .291
Very funny, but someone might actually believe you, so add a smiley
.Very funny, but someone might actually believe you, so add a smiley
Hey it's no joke Juster!
Check it out on some external balistics software. It really works!
I think if I recall wind wind drift is the same in MOA on the scope, but not by total inches of wind drift.
I have the charts somewhere if I can find them.
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Then words fail me. Luckily, your theory cannot be put to any practical use.
Geometry is a harsh mistress.
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Dats vewey vewey funny....
I just pulled a couple bullets up on RCBS.Load
1 is a .231 BC and the other .485 BC both at 3000 FPS, the software says for the .485 BC the velocity at 480 yards is 2149 FPS and the .231 BC at 230 yards is 2124 FPS. I think that's close enough.
For 10 mph wind the software says 12.6 inches at 480 yards for the .485 BC and 4.63 inches for the .231 BC at 230 yards. That works out to just over 2 MOA at 231 and 2.5 MOA at 480 yards. Not exactly the same but pretty darn close.
I just pulled a couple bullets up on RCBS.Load
1 is a .231 BC and the other .485 BC both at 3000 FPS, the software says for the .485 BC the velocity at 480 yards is 2149 FPS and the .231 BC at 230 yards is 2124 FPS. I think that's close enough.
For 10 mph wind the software says 12.6 inches at 480 yards for the .485 BC and 4.63 inches for the .231 BC at 230 yards. That works out to just over 2 MOA at 231 and 2.5 MOA at 480 yards. Not exactly the same but pretty darn close.
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ARS nailed it.
The drag curve of a G1 bullet and a G7 bullet are very different from each other.
If you are shooting well inside your super-sonic range then you will be fine using a G1 BC. But when you drop into the trans-sonic (below 1400FPS) stage of bullet flight the error that you get using a G1 BC will grow.
If you have the G7 data and a calculator that supports it then there is no reason not to use G7.
rnbra-shooter
CGN Ultra frequent flyer
- Location
- New Brunswick
The gun-sim blog article that Juster linked to describes it very well, pictorially. A Berger 190 is a modern, slender-nosed boattail bullet. A G7 drag coeff. will work fairly well with it.
To the OP: before you fuss about using G1 or G7, you need to know your muzzle velocity, and also pay _some_ attention to temperature and altitude (and it goes without saying, range to target).
At distances of 600 yards or closer, G1 and G7 will work equally well. Even though G1 is 'wrong', the errors are so small that they'll never show up or cause you any problems.
If you are shooting at 1000 yards, G1 will get you predictions good to within a minute or so, most of the time. For most purposes this is more than good enough. Using G7 will be substantially more accurate (if that matters).
To the OP: before you fuss about using G1 or G7, you need to know your muzzle velocity, and also pay _some_ attention to temperature and altitude (and it goes without saying, range to target).
At distances of 600 yards or closer, G1 and G7 will work equally well. Even though G1 is 'wrong', the errors are so small that they'll never show up or cause you any problems.
If you are shooting at 1000 yards, G1 will get you predictions good to within a minute or so, most of the time. For most purposes this is more than good enough. Using G7 will be substantially more accurate (if that matters).
The Berger reloading manual explains this fairly well if I remember correctly. They even list the G1 and G7 BC for each bullet along with their recommendation for which one to use for each bullet. They basically recommend the G1 for the flat base bullets and G7 for the boattails.
