2. Check Range

Source: Core Rulebook 3E, p. 47

Step 2 of shooting: each firing model must measure to the nearest model in the target unit and be within its weapon's maximum range.

All weapons have a maximum effective range that tells you the furthest distance they can shoot. If your target is beyond this maximum range then your shot misses automatically. This is why you have to choose your target before measuring the range.

Weapon Maximum Range
Shuriken Catapult 12"
Laspistol 12"
Boltgun 24"
Autocannon 48"

When checking range, measure to the nearest model in the target unit. Models in that unit who are out of range cannot be hit, as described in Casualty Removal later.

When a unit fires, measure the distance for each model in the unit. Any that are out of range may not shoot.

Diagram: Measuring Range — a Space Marine with a boltgun (24" range) stands at the bottom of the battlefield with a 24" arc drawn forward. Four Dark Eldar warriors within the arc are in range and may be hit; four other Dark Eldar warriors positioned beyond the arc are out of range and may not be hit.