%halfcock%

v. t. [ imp. & p. p. Halfcocked p. pr. & vb. n. Halfcocking. ] To set the cock of (a firearm) at the first notch. [ 1913 Webster ]

To go off half-cocked,
To go off halfcocked. (a) To be discharged prematurely, or with the trigger at half cock; -- said of a firearm. (b) To do or say something without due thought or care. [ Colloq. or Low ] [ 1913 Webster ]