.50 Caliber BMG Regulation Act of 2004
The .50 Caliber BMG Regulation Act of 2004 is a law in the state of California that effectively banned all .50 BMG-caliber rifles from being sold in the state. The law took effect on January 1, 2005.
Source: Wikipedia — .50 Caliber BMG Regulation Act of 2004 (CC BY-SA 4.0)