No one will officially admit what the “HST” stands for. Is it “Hydra Shok Two” or is really just a meaningless set of three letters?
The initial patent applications were filed in November 2000, and Federal’s Douglas W. Carr and Lawrence P. Head received US Patent #6,805,057 in October 2004. By that point, Federal had already included the new HST loads in its 2004 LE products catalog.
At SHOT Show 2013, Federal announced its civilian Personal Defense line of HST loads.
The follow link will take you to a classic “The Gun Zone” article featuring high-speed photography from Tom Burczynski. Burczynski reportedly consulted on the HST, but as you can see, his name was not specifically credited in the patent, except as prior art.