Hornady first started to advertise their eXtreme Terminal Performance (XTP) projectile in 1990. It appears to have been an evolution of their 1988-vintage Rapid eXpansion Tip (RXT) line. Their goal was 1.5x diameter expansion at a wide range of velocities. If you look closely at their advertisement, you’ll note that they did not use the Fackler-developed/FBI-approved 10% gelatin mix or even the older 20% gelatin mix. Rather they relied upon water and a grease/wax mixture, the latter of which was apparently their standard testing material for over 15 years.
The next step in the XTP’s evolution came in 1999, when Hornady engineer Dave Emary reportedly first started playing with filled hollowpoint cavities. The first were made using off-the-shelf silicone caulk from a local hardware store. However, the next step was away from handgun projectiles and on to rifle applications, with the creation of a flexible ballistic tip insert – Hornady’s Flex-Tip (FTX) projectile. The goal here was to offer a pointed tip projectile that was safe to use in tubular magazines. The patent application was filed in May 2005, and awarded in June 2008.
Hornady FTX LEVERevolution patent:
It was only a brief matter of time before the pointed FTX insert was moved over to handgun projectiles in cartridges like the .357 Magnum and .44 Magnum, which saw dual use in handguns and lever-actions. But once the FTX concept was in production and popular, Emary moved back to concentrate upon a flush tip FTX insert design, circa 2008. While part of the FTX line, the name Critical Defense would ultimately be applied.
Then came Emary’s next step, tweaking the FTX design to meet the FBI’s demanding barrier test requirements. Emary fell back upon an earlier Hornady concept, the InterLock jacket, to mechanically lock the core to the jacket. To match the FTX branding, this became known as the FlexLock. Introduced in 2012, the new Critical Duty line uses a thicker jacket and a harder lead core than the earlier Critical Defense line.
Hornady Critical Duty patents: