Region: US | Usage example: He announced new features before testing; he went off half cocked.

Go off half cocked

Meaning

Act prematurely or without enough preparation.

Used when someone leaps into action too soon.

Origin notes can vary by region and source; this page gives the commonly reported explanation and usage context.

Firearm reference to the hammer not fully cocked, causing misfire.

Appeared in American frontier speech in the early nineteenth century.