With the exception of (I think) Vermont you cannot legally have a loaded weapon in your vehicle. CCW (for your state) gives you a legal right to carry a loaded weapon without violating your state law.
Under federal law you are required to carry the gun and ammunition seperately or as separately as your vehicle will reasonably allow. The firearm must be in a locked case and the ammo separated from the weapon. CCW allows you the right to carry under federal law.
Check with a lawyer (I am not one) but unless you live in Vermont I definitely strongly advise against carrying a loaded weapon in a vehicle without a CCW permit. Why risk a felony not to have the permit that you (in my opinion) have a legal right to so long as you go through the legal process.