571.030
(4) Exhibits, in the presence of one or more persons, any weapon readily capable of lethal use in an angry or threatening manner; or
(5) Has a firearm or projectile weapon readily capable of lethal use on his or her person, while he or she is intoxicated, and handles or otherwise uses such firearm or projectile weapon in either a negligent or unlawful manner or discharges such firearm or projectile weapon unless acting in self-defense;
(10) Carries a firearm, whether loaded or unloaded, or any other weapon readily capable of lethal use into any school, onto any school bus, or onto the premises of any function or activity sponsored or sanctioned by school officials or the district school board.
to me, readily capable of lethal use means it is ready to fire. i think this means at least a round is chambered.
having your clip in, but not having a round chambered would not count.
having to flip the safety and run the slide to chamber a round does not seem readily capable. this was added in the 28th mainly to deal with the use of alcohol and having a firearm.