September 5th, 2019
G1 vs. G7 Ballistic Coefficient Models — What You Want to Know
More than the previous 12 months, this report was one particular of the Major TEN most-study Each day Bulletin capabilities. We’re reprising it these days for these who may perhaps have missed it the initially time. The above diagram comes from a TiborasurasRex YouTube Video comparing G1 and G7 BC models. CLICK Right here to watch the video.
The improved, up-to-date ballistics applications let you choose either G1 or G7 Ballistic Coefficient (BC) values when calculating a trajectory. The ballistic coefficient (BC) of a physique is a measure of its capability to overcome air resistance in flight. You have in all probability observed that G7 values are numerically reduce than G1 values for the identical bullet (commonly). But that does not imply you need to choose a G1 worth just due to the fact it is greater.
Some readers are not very confident about the distinction amongst G1 and G7 models. One particular forum member wrote us: “I went on the JBM Ballistics web page to use the internet-primarily based Trajectory Calculator and when I got to the component that offers you a selection to decide on amongst G1 and G7 BC, I was stumped. What determines how, or which one particular to use?”
The uncomplicated answer is the G1 worth commonly performs improved for shorter flat-primarily based bullets, although the G7 worth need to perform improved for longer, boat-tailed bullets.
G1 vs. G7 Ballistic Coefficients — Which Is Ideal for You?
G1 and G7 refer each refer to aerodynamic drag models primarily based on distinct “standard projectile” shapes. The G1 shape appears like a flat-primarily based bullet. The G7 shape is very distinct, and improved approximates the geometry of a contemporary extended-variety bullet. So, when selecting your drag model, G1 is preferrable for flat-primarily based bullets, although G7 is ordinarily a “better fit” for longer, boat-tailed bullets.
Drag Models — G7 is improved than G1 for Lengthy-Variety Bullets
Quite a few ballistics applications nonetheless supply only the default G1 drag model. Bryan Litz, author of Applied Ballistics for Lengthy Variety Shooting, believes the G7 regular is preferrable for extended-variety, low-drag bullets: “Part of the purpose there is so significantly ‘slop’ in advertised BCs is due to the fact they’re referenced to the G1 regular which is incredibly speed sensitive. The G7 regular is a lot more suitable for extended variety bullets. Here’s the final results of my testing on two low-drag, extended-variety boat-tail bullets, so you can see how the G1 and G7 Ballistic coefficients evaluate:
G1 BCs, averaged amongst 1500 fps and 3000 fps:
Berger 180 VLD: .659 lb/in²
JLK 180: .645 lb/in²
The purpose the BC for the JLK is much less is largely due to the fact the meplat was drastically bigger on the distinct lot that I tested (.075″ vs .059″ see attached drawings).
For bullets like these, it is significantly improved to use the G7 regular. The following BCs are referenced to the G7 regular, and are continuous for all speeds.
Berger 180 VLD: .337 lb/in²
JLK 180: .330 lb/in²
Quite a few contemporary ballistics applications, like the no cost on the internet JBM Ballistics System, are capable to use BCs referenced to G7 requirements. When accessible, these BCs are a lot more suitable for extended variety bullets, according to Bryan.
[Editor’s NOTE: BCs are normally reported simply as an 0.XXX number. The lb/in² tag applies to all BCs, but is commonly left off for simplicity.]
Tags: Ballistic Coefficient, ballistics, Berger Bullets, Bryan Litz, Bullet Drag, Drag Model, G1, G7, G7 Model, Lengthy-Variety, Trajectory