Heat Shield Technology
Why are the drag curves convex nearly immediately if the effects are only significant at longer ranges?
For most projectiles, the effect of the tip beginning to change shape is nearly immediate. From the graph of the drag coefficient (Cd) vs. distance above, you can see that the change in the drag of the projectile starts to happen immediately and accelerates until it stabilizes at about 300 yards. This is for a high ballistic coefficient (BC) bullet, over a 0.300 G7. The effect is short-lived and not as severe for lower BC projectiles. With low-BC projectiles, like varmint bullets even at high velocity, the effect is virtually nonexistent. It should not be hard to visualize that a change of 4 to 6% in the drag of a moderate BC projectile over 200 to 300 yards, that is intended for 300- to 400-yard shooting, would not see much effect on the ballistics.
However, a change of 8 to 12% on a bullet intended to be fired to ranges of 800 to 1,000 yards will see a far greater effect on its ballistic performance. Drop and wind drift are functions of projectile drag and time of flight. Using JBM ballistics and Doppler radar data for the two projectiles discussed above, the Delrin-tipped projectile has a G7 of 0.281 over 400 yards and 0.273 over 1,000 yards. The Heat Shield™-tipped projectile has a G7 BC over 400 yards of 0.312 and a G7 BC of 0.301 over 1,000 yards. This shows the change in BC, of any standard, that does not match the drag performance of the projectile it is attempting to model. This is why drag coefficient is the only way to accurately analyze what is happening.
Using the above G7 radar calculated BCs, the difference in point of impact for the two projectiles at 400 yards is 0.2 minute of angle (MOA). The difference in point of impact of the two projectiles at 1,000 yards is 1.9 MOA. It doesn’t really matter at shorter ranges but is very important for longer-range shooting. Calculating trajectories using the actual drag coefficient vs. Mach, the differences at distance are even greater. Shooting the two different projectiles at 400 and 1,000 yards gave results very close to those calculated. The effects, at shorter ranges, for lower BC projectiles is even less. For existing standard type hunting and varmint projectiles, with current tips, this doesn’t matter. That is not the case for long-range match and hunting and shooting situations.