Missouri firearm laws
Missouri has a "peaceable journey" under Missouri Statutes 571.030 which law says it is legal to carry the weapon in a passenger compartment of a vehicle as long as (1) the concealable firearm is otherwise lawfully possessed, (2) the person is 21 or older, or (3) the person is in his dwelling unit (e.g. RV) or upon premises over which the person has possession/authority/control, or is traveling in a continuous journey peaceably through this state.
The same applies (it is not a crime) when the person is 21 and possesses an exposed firearm for the lawful pursuit of game.
Open carry
Missouri does allow open carry of firearms for those age 18 or older. However, city, county, and municipalities are allowed to pass laws and ordinances restricting this. It is advisable to check local laws and ordinances before openly carrying a firearm within Missouri.
Concealed carry
Missouri Statute 571.070 (8/28/2007) says that it is unlawful for a felon or adjudged incompetent Person to have possession of any firearm (including concealable firearms). Violation of this law is a class C felony.
Missouri Law Exempts the possession of antique firearms, as defined in 18 U.S.C. Section 921, from the provision that specifies a person commits the crime of unlawful possession of a firearm if he or she is a convicted felon possessing a firearm (Section 571.070).
Missouri Statute 571.121 (8/28/2007) says (a) you have to carry permit with you when you carry the concealed weapon and if you don't have it with you, it is not a crime, but you can be fined up to $35, and (b) director of revenue issues a driver's license or a state I.D. with a CCW endorsement that reflects that you can carry concealed.