The combi-bolter is the standard armament for Chaos Space Marine Terminators. However, it is not uncommon to find them mounted on Chaos Space Marine vehicles for additional firepower. Pintle-mounted combi-bolters are located on the outside of a vehicle and can be used by crewmen from an open hatch or by remote control from inside the vehicle. They are treated as an extra twin-linked bolter which may be used in addition to any other weapons the vehicle can fire. This means that a vehicle that moves can fire one weapon and also the pintle-mounted combi-bolter.
Pintle-mounted Combi-bolter
Source: Codex: Chaos Space Marines (1999), p. 21