The Supreme Judicial Court rejected Tuesday challenges to the state’s gun storage law, finding that it is ‘‘reasonably designed’’ to prevent unauthorized people from gaining access to guns and does not violate the Second Amendment right to keep them for self-defense in the home. The law requires that guns not under the immediate control of their owners be stored in locked containers or that they be equipped with a safety device that makes them inoperable by anyone other than the owner or authorized users. John McGowan of Springfield was charged with violating the storage law after his roommate took McGowan’s loaded handgun out of an unlocked bedroom drawer and threw it in the bushes outside.