Question: In the one episode Gabriel attempted to kill Lucifer with his archangel blade. Even though he didn't succeed, why didn't they attempt to do use one before? Couldn't Cas have given them one, or gotten one if an archangel's blade is different then an angel blade (I'm not sure), or would it have even killed Lucifer, because he is an angel after all?
Answer: Angel blades come from angels. It's their angelic magic that makes it special. Therefore, an archangel blade is made magical with the powers of an archangel. They couldn't have just created one or used one, as none of them are archangels.
Question: The crew takes a private jet to most locations but always have the same black S.U.V.s. How do the vehicles get there as fast as the crew?
Chosen answer: Black SUVs are common police, military and dignitary vehicles around the world. It is not too much to assume they could be rented or owned by the police forces in the areas.
Other people have explained it but fore more information, federal cars would most likely be brought to the airport from the nearest agency, so they can drive out to their locations especially in rural situations.
Answer: There is only one BAU (or that's the impression the show gives, in reality there's 5 teams within the BAU), and they're based out of Quantico. However, the FBI has 56 field offices, each with their own vehicles leased from the over 200,000 vehicles that make up the Federal motor fleet. There are long term leases to federal agencies on these cars, in addition to there always being vehicles being made available to lease on an ad hoc basis for assignments. Plus, local and state police likely also have their own unmarked fleets, but due to the vehicles being mostly the same make/model/color in most episodes, they'd likely be borrowed from the nearest field office or other local federal office or ad hoc leased from the fleet for the assignment.
Question: In a few episodes, the FBI agents will walk into a room and say "smell that?" and the reply is "shots fired", supposedly because they can smell the distinct odor of burnt gunpowder. Then they'll look behind a desk and find a dead body in a pool of blood. But wouldn't the smell of a dead person, or the blood, be way more overpowering? Or would it take too long for a dead body to start to smell? And how long would the smell of gunfire in an enclosed room last?
Answer: Because of coincidence.