SpecificallyL
"Each time a model equipped with both a Pistol and another type of ranged weapon (e.g. a Pistol and a Rapid Fire weapon) shoots, it can either shoot with its Pistol(s) or with all of its other weapons. Choose which it will fire (Pistols or non-Pistols) before making hit rolls."
So oddly, if you had a Rapid Fire and a Heavy weapon, you could fire bothg. Its only Pistols that make it difficult.