How much does the G1 or G7 BC change over the flight of the bullet? The main idea here is that BC can change with velocity. As the bullet slows down at long range, the BC value changes. A BC that’s valid at high speed near the muzzle, might be very different from the BC at long range when the bullet has slowed to ½ its initial speed. Understanding how the BC changes with speed is important to calculating accurate trajectories. Additionally, some bullet manufacturers choose to only advertise the BC at high speed for marketing purposes, even though that’s not the average performance of the bullet at long range, and will not result in accurate trajectory predictions if used in ballistic software. We will cover this subject in more detail when we release the article Variation in BC with Velocity in the coming weeks.