8.2.1 - Snap Shots
Core Rules, p. 21
A Unit may sometimes be forced to make Snap Shots instead of a regular shooting attack. Snap Shots are resolved as a regular shooting attack, except all 'To Hit' rolls are resolved at Ballistic Skill (BS) of 1. A Snap Shots Ballistic Skill (BS) characteristic may never be modified, but re-rolls are permitted.
Snap Shots may never be taken by weapons with the Blast or Large Blast special rules.