If a model has BS6 or higher, it gains a re-roll should it fail to hit whilst shooting. The second roll usually has a lower chance of hitting. On the table below, the first target number given is for the first roll, the second is the target number when re-rolling:
Ballistic Skill | 6 | 7 | 8 | 9 | 10 |
D6 roll To Hit | 2+/6+ | 2+/5+ | 2+/4+ | 2+/3+ | 2+/2+ |