Changes the offense of weapons possession by adding high-capacity firearm magazines

HB 878 changes Missouri law by making it illegal to possess a "high-capacity magazine" (defined as a magazine holding more than ten rounds of ammunition). This directly affects individuals who own or carry such magazines, as it becomes a class D felony offense. The bill adds this specific provision to existing weapons possession laws, with exceptions for law enforcement, military personnel, and certain commercial or display activities under federal law. It does not change penalties for other weapons listed in the law.