The Ballistic Coefficient (BC) question

[PA BEN]

The Nosler web site says to use G7 BC for their Accubond long range bullets. I ordered their newest reloading book that has reloading data for the new long range accubond. The long range box has the G1 and G7 BC for the bullet. The BC chart in the book I have doesn't say G1 or G7? The G7 BC is half of the G1 BC, so it doesn't seem to make sense using the lower number. As you can tell I'm all confused, any help would be great. Thanks

[jrebel]

I don't pay any attention to the listed BC G1 or G7.....quite often they are not accurate anyway.  Find a load your rifle likes, shoot and find your velocity and then set your calcualations from there.  Shoot at all listed ranges to confirm or tweek your calculation. 

I know some may argue the statements above....but this is my experience.  Also....recently I have found the ABLR is finicky and seems to like a little longer jump.   

[yorketransport]

You can use the the G1 BC as a starting point and then come up with your own "trued" G7 BC using Jrebel's method to get it more accurately dialed in. I haven't really had an issue using G1 BCs unless I'm dealing with bullets going transonic.

The other option is to use the JBM calculator. This is an excellent resource.
http://www.jbmballistics.com/cgi-bin/jbmtraj_simp-5.1.cgi

[BULLBLASTER]

THe g1 and g7 calculions are different in your calculator. I prefer to use the g7 number and start with what the box says but then true it with shooting in known conditions and known velocity.

If you don’t have accurate conditions data (pressure, temp, shot angle), trueing your bc to velocity won’t help you much.

[PA BEN]

From the Nosler website

Newly Updated BC'S
New for 2018, we have had the Ballistic Coefficients (BC’s) of our AccuBond-Long Range (ABLR) bullets tested and verified with Doppler radar. This has resulted in a revision of our published BC numbers to more accurately match real-world flight characteristics. Using Doppler radar to verify our BC’s allows us to provide the most accurate BC numbers to our customers while increasing the accuracy of long range ballistics calculations. To perform this critical testing, we selected the Energetic Materials Research and Testing Center (EMRTC) at the New Mexico Institute of Mining and Technology. EMRTC is the largest privately owned ordnance and ballistic test facility outside the government, encompassing 40 square miles and over 30 test ranges. EMRTC is internationally recognized as a center for excellence in energetics and ballistics research and testing. We are pleased to provide these highly accurate BC numbers and feel confident that they will bring a new degree of precision to your long-range ballistics calculations. For the utmost accuracy, we recommend using the G7 BC when calculating trajectories with the ABLR bullet line.

[SilkOnTheDrySide]

G7 isn’t “half” of G1s. It’s a different number that used in a completely different equation.

If I remember right it was created by Brian Litz at Berger to more accurately describe the varying BCs over the arc of a bullet, especially with boat tailed bullets. (This is off memory, so verify at your own risk).

What I like to do after I find a solid load, is to verify speed, then shoot in 100 yard increments out to 1300 yards.

Once I’ve done that and have my MIL adjustments at each yardage, I play with the G7 number to make them all match up.

On my previous barrel for example, I used .349 G7 BC for my 195 Bergers.


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[jasnt]

G1 or g7 is the calculation equation used to tell your ballistic calculators what math equation to use.  Even tho the g7 number is smaller it is best to use for boattail bullets. If you never shoot past 600-700 yards you may not notice a difference between the two. Closer you get to transonic flight the more you see the diff

https://m.youtube.com/watch?v=gjzs79kDr6E