Originally Posted By: fw707Hey Cat,
how does velocity affect BC numbers?
The way the air flows over the bullet changes with different speeds.
At high speeds the boat tail and flat base behave the same - like flat based bullets. The tail drag is the same area of the base times 14.7 pounds. So I bullet that has a .20" inch area at bore diameter, and a .20" base area... it has a constant tail drag of 3 pounds, until it hits around 600 fps and then it slowly changes.
But a boat tail bullet that has a .20" inch area at bore diameter, and a .10" base area, has tail drag of 3 pounds at very high velocity (3,000+ fps-ish) - but when the velocity gets to the point where the air is starting to follow the slope of the boat tail, the drag starts diminishing, and continues to get less and less as the bullet slows.
As the speed slows, the boat tail bullet has less tail drag... and as Martha Stewart says, "... and that is a good thing!"
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