Heavy Bolter

Unless it also contains a Techmarine, an unengaged unit that contains at least one model with this special rule must roll a D6 at the start of its turn. On a 4+, this special rule has no effect this turn. On a 1, 2 or 3, the unit is mindlocked until the start of its following turn. A mindlocked unit may not voluntarily move, shoot or charge, but must still complete compulsory moves, such as Pile In and Fall Back moves.