What is the most illegal knife in the US?

The ballistic knife is the most heavily restricted knife in the US. A ballistic knife fires its blade from the handle, and that launch mechanism places it in a more restricted legal category than normal fixed blades, folders, or many automatic knives. Federal law directly targets ballistic knives, and some states add their own bans on possession, sale, or carry. That combination makes it the knife most likely to create serious legal problems across jurisdictions. Other knives, including switchblades, butterfly knives, and daggers, face mixed rules that change by state and city. The ballistic knife stands out because the federal restriction is specific, direct, and unusually severe.