Heat Shield Technology

Would insufficient spin rate cause what you're seeing in the drag behavior of some of these projectiles?

In situations involving extreme lack of gyroscopic stability (Sg), effects similar to what we witnessed could contribute to the effects we observed. Extensive radar testing proves this is not what is occurring. We perform extensive bullet modeling for both mass and aerodynamic properties using state-of-the-art, military-grade software called PRODAS, which has been in use since the early 1970s. This allows extremely accurate and high-definition modeling of projectile flight performance and predictions of stability. We have been using this software since the early 1990s. We have been using Sg for analysis of projectile stability and determination of appropriate twist rate for several decades. We generally design for a worse case Sg of 1.5 under cold, dense atmospheric conditions to allow margin for variability in twist rates.  All projectiles tested and data presented were tested under conditions in which the Sg was in the 1.8 to 2.1 range. For example, in the graph shown, the 7 mm 175-grain Hornady and Nosler bullets were fired from a 7 mm Remington Magnum with a 1-9.25” twist, and the Sgs were 2.05 and 1.95 respectively for the atmospheric conditions. To further put this question to bed, Figure 1 shows the radar generated drag coefficient (Cd) vs. Mach number graph at supersonic Mach numbers for identical 6.5 mm 140-grain ELD™ Match projectiles that were literally made serially with the only difference being the tip material. They were both fired from the same 6.5 mm Creedmoor rifle at approximately 2,780 feet per second (fps), with a 1-8” twist, within seconds of each other. The Sg for these projectiles in the atmospheric conditions was 1.80. These projectiles had enough spin to be adequately stabilized.

ELD Match Cd vs Mach
As can be seen from the graph, the Heat Shield™-tipped projectile has a very normal looking drag curve. The Delrin-tipped projectile immediately sees a rapid rise in drag as compared to the Heat Shield™ projectile and maintains this higher level of drag offset until low supersonic Mach numbers, where the Meplat diameter has much less of an effect on drag. The two plots do not start at the same place at high Mach numbers because of the separation, offset, between the radar head and the rifle. (You can’t shoot through the middle of the radar head. That would be a very expensive mistake.) It takes the projectiles 40 to 50 yards to fly into the radar beam. The projectiles are acting exactly like they should for what is happening to them or not happening to them. This phenomenon is happening to everyone’s polymer-tipped projectiles, not just ours.