February 13, 2022. This article was one the TOP 20 most-read Daily Bulletin articles for the past 12 months. For those who missed it, we’re republishing it today. The diagram above is a TiborasurasRex YouTube video that compares G1 and G7 BC models. CLICK HERE to view the video. The most up-to-date ballistics software allows you to choose between G1 and G7 Ballistic Coefficients (BC) values for calculating a trajectory. The body’s ballistic coefficient (BC), is a measure its ability to overcome air resistance during flight. G7 values for the same bullet are typically numerically lower than G1 ones. However, this doesn’t mean that you should choose a G7 value for the same bullet just because it is more numerically. One forum member wrote: “I went to the JBM Ballistics website in order to use the web-based Trajectory calculator, and when I reached the section that allows you to choose between G1 or G7 BC, it was confusing. Which one or how do you choose? The G1 vs. the G7 Ballistic Coefficients – Which is Right for You?
G1 and G7 are aerodynamic drag models that are based on specific projectile shapes. The G1 shape is similar to a flat-based bullet. G7 is a different shape and more closely resembles a modern long-range round bullet. G1 is preferred for flat-based bullets, whereas G7 is more suitable for long-range bullets with a longer tail.
Many ballistics programs offer only the G1 drag model. Bryan Litz, author Applied Ballistics for Long Range Shooting believes that the G7 standard is better for long-range, low drag bullets. “Part of why there’s so much’slop in advertised BCs is that they’re referencing the G1 standard, which is very speed sensitive. G7 is better suited for long-range bullets. Here are the results of my testing with two long-range, low-drag boat-tail bullets. You can compare the G1 BCs and G7 Ballistic coefficients.
Berger 180 VLD: 0.659 lb/in2
JLK 180: 0.645 Lb/in2The BC for the JLK is lower because the meplat on the lot I tested was significantly higher (0.075?). vs. 0.059 vs 0.059? These BCs are consistent for all speeds and are referenced to G7 standards.
Berger 180 VLD: 0.337 lb/in2
JLK 180: 0.330lb/in2 Many modern ballistics programs, such as the JBM Ballistics Program online, can use BCs that are compliant with G7 standards. Bryan says that these BCs are more suitable for long-range bullets when they are available. [Editor’s Note: BCs are usually reported as a 0.XXXX number. The lb/in2 tag is applicable to all BCs but it is often left off for simplicity.
Similar Posts
