I found a bug where you can drive around with your gun equipped, I know this would be implemented for handguns, but a sniper isn’t that realistic.
When you equip the weapon before you enter the vehicle and then go inside the vehicle, you can drive with your dual-handed weapon equipped.
This means you can shoot with a dual-handed weapon while driving, which is impossible.
Looks like more of an oversight than a bug. Making two-handed weapons automatically holster when entering a car is an important detail, but probably not important enough to warrant it being added before more important stuff.
The limitation that prevents you from using a two-handed weapon as a driver has not been implemented yet (similar to how it was a while before Nelson added proper limits to magazine capacity).
While it is a valid concern, Nelson has been aware of it for months now and will likely get around to fixing it once he’s done with other higher priority implementations.