Let's go right to the source Warhammer 40,000:
Let's review what this means for your Sternguard, 1st Company Veteran Heroes of the Imperium.
1. You can move, and then you can still shoot up to the maximum range of the weapon.
2. If your unit is divided between ranges, you just measure to see who can still Rapid Fire.
3. Vengeance Rounds will Rapid Fire at only 9", while Kraken bolts can reach 15" to Rapid Fire.
4. If you shoot with a Rapid Fire weapon, you may not assault.
5. If you want to assault, you need to use your standard issue bolt pistols, upgraded pistols or
assault weapons like meltaguns.