Long guns cannot be carried loaded in a vehicle. "Loaded" means a round in the chamber. A loaded mag, but empty chamber, is legal. This is part of the hunting laws. NRS 503.165.
Handguns, except in North Las Vegas and Boulder City, can be carried loaded in the car, if not concealed. Of course, for CCW holder, handguns can be transported loaded and concealed in the car.
In North Las Vegas and Boulder City, anyone without a CCW should have those handguns unloaded and locked in an inaccessable container.