The Firearms Owner's protection Act, a federal law, is supposed to protect you when traveling in ANY state, but some jurisdictions, particularly on the east coast, don't seem to care. Under FOPA, it is legal to travel with an unloaded firearm in a locked container. AFAIK, the FOPA does not require ammo to be in a separate container, but as others have noted, apparently Md disagrees. I don't have a link right off, but the following is a TRUE story: a florida man, his wife and children were returning to Florida after visiting relatives in NJ. After exiting a tunnel , they were followed by a Md. trooper of some type who eventually pulled the vehicle over, allegedly for "speeding." it appears that the officer had run the plates while trailing this Florida vehicle and determined that the driver had a CCW. The FIRT thing the officer did when he got to the driver's side window was to demand where the weapon was. It was actually in Florida in a safe, but the officer didn't believe it, called in back up, and searched the vehicle. All of this was perfectly illegal, but that didn't seem to matter.
D.C. is a world of its own, and a world of hurt. If you pass through there, make sure EVERYTHING is in a locked container, and refuse consent to ANY search, no matter how many threats the office makes. Under D.C. law, a gun includes not just the gun, but any ammunition, or component of ammunition, INCLUDING spent casings. if you have any of these items in the District, you have violated the city codes and are subject to arrest, unless it just so happens that the firearm is registered in the City, or the ammunition or components will fit in a firearm registered in the City. Kind of unlikely if you live in another state. A recent trial court decision held that the City's ban on concealed or open carry of firearms is unconstitutional, but that decision has been stayed for 90 days to allow the City to pass a compliant carry law. (the city has already vowed to appeal.) The rational of the case should apply to carrying firearms in locked containers, since the City cannot and should not be allowed not override federal law. Then again, New York City has been doing it for years and getting away with it unless you are willing to spend thousands of dollars to hire an attorney to get the case dismissed.