Hydra-Shok is a type of bullet used in commercial self-defense ammunition made by Federal Cartridge

Federal Cartridge

Federal Cartridge is a wholly owned subsidiary of Alliant Techsystems, located in Edina, Minnesota. With a work force of nearly 1,000 in Anoka, Minnesota, Federal manufactures a complete line of shotshell, centerfire, and rimfire ammunition and components....

. It was originally patented by bullet designer Tom Burczynski. Hydra-Shok bullets feature a unique, patented center-post design and notched jacket. Together they are meant to provide more reliable expansion and deeper penetration. Center post designed bullets like Hydra-Shok have more predictable results and therefore offer some advantage as a defensive bullet. In ballistic gelatin

Ballistic gelatin

Ballistic Gelatin is a testing medium scientifically correlated to swine muscle tissue , in which the effects of bullet wounds can be simulated. It was developed and improved by Martin Fackler and others in the field of wound ballistics. Ballistic gelatin is a solution of gelatin powder in water...

, the bullet typically displays very rapid expansion resulting in a larger but more shallow wound channel than would be typical from most other bullet configurations in the same caliber and of similar weight.

The Hydra-Shok bullet is available in various calibers; 9 mm, 10 mm, .32 ACP, .380 ACP, .38 S&W Special, .357 Magnum, .40 S&W, .45 ACP, .45 GAP, and .44 Magnum. It can also be found in 12ga. shotgun slugs. (http://www.federalpremium.com:80/m/product_listing.aspx?f=2&t=2&b=31)
The Hydra-Shok bullet is a hollow point round. These rounds are anti-personnel, meaning they for use against human or other organic targets. A normal bullet has a smooth, rounded tip designed for accuracy and penetration. A hollow point round, however, has a hollow tip that causes it to expand upon impact. The expansion of the bullet increases its stopping power, the force at which it makes contact with its target. The Hydra-Shok bullet is designed to have minimum penetration and maximum stopping power which makes it very effective as a defensive bullet.