halfcock

half +‎ cock

halfcock (uncountable)

1. The position when the cock of a gun as at the first notch.
   • 2010, Patrick Sweeney, 1911 The First 100 Years: The First 100 Years

     This was bad both for the alibi reshoots it caused and subsequent delays in a match, but if the hammer fell to halfcock enough times, the half-cock notch would mar the sear tip, adversely affecting trigger pull.

halfcock (third-person singular simple present halfcocks, present participle halfcocking, simple past and past participle halfcocked)

1. To set the cock of (a firearm) at the first notch

• go off halfcocked