umm a "crime of passion" is the definition of manslaughter as i understand it ie walking in to find your wife screwing the cable guy (sorry watching NCIS again) and you "snap" and kill them both. Not murder because there was no planning (how could there be if you didnt know she was sleeping around) means manslaughter
It all depends on where you keep your gun. In a holster on your belt? Manslaughter. In a gun safe with an eight digit PIN? murder.