Caliber convertible AR-15 upper receiver system

A caliber convertible, upper receiver system for a magazine-equipped, manually operated or semiautomatic or fully automatic firearm, said upper receiver system being adapted to replace the original equipment upper receiver portion and to attach to the original equipment lower receiver portion of said firearm in order to render the firearm capable of firing either a first cartridge or a second cartridge, the first and second cartridges having dissimilar calibers, the system comprising:

• an upper receiver assembly attachable to the lower receiver portion of the firearm, said assembly including
• a charging handle;
• and
• an upper receiver extending longitudinally from a rear end to a front end and having a longitudinally-extended, upper channel portion into which the charging handle is insertable through a rear opening thereof and a pair of side walls coextensive with the channel portion and depending therefrom that define a substantially cylindrical interior space, open at the bottom, and an externally threaded, cylindrical extension at a front end of the upper receiver that is coaxial with said interior space;
• a barrel assembly extending longitudinally from a rear, firing chamber end to an opposite, front end, said barrel assembly including
• a barrel having a straight, cylindrical bore;
• and
• means to attach said rear end to the upper receiver assembly, adjacent to and aligned with the firing chamber;
• a first barrel liner dimensioned for insertion into the barrel bore and to receive at a rear, firing chamber end thereof a bullet fired from the first cartridge in the firing chamber, and to conduct the bullet through the barrel assembly and out an opposite, front end of said barrel liner, said first barrel liner including
• a first barrel liner head at the rear end of said liner, said head having a longitudinally-directed aperture for receiving a bullet fired from the firing chamber, and
• a first liner tube that extends longitudinally from said head to the front end of the first liner, said tube having a bore aligned with the aperture of said head;
• a second barrel liner dimensioned for insertion into the barrel bore and to receive at a rear, firing chamber end thereof a bullet fired from the second cartridge in the firing chamber, and to conduct the bullet through the barrel assembly and out an opposite, front end of said barrel liner, said second barrel liner including
• a second barrel liner head at the rear end of said liner, said head having a longitudinally-directed aperture for receiving a bullet fired from the firing chamber, and
• a second liner tube that extends longitudinally from said head to the second end of the second liner, said tube having a bore aligned with the aperture of said head;
• a bolt adapter carrier assembly insertable into the cylindrical interior space of the lower receiver, said assembly including
• a bolt that carries a spring-loaded firing pin mounted for reciprocal, longitudinal movement within a firing pin bore of the bolt, and
• means for attaching and disattaching alternately the head of either the first or the second barrel liner to said carrier assembly;
• and
• a magazine adapter insert dimensioned for insertion and retention within the magazine of the firearm and adapted to receive and store a plurality of the first or second cartridges for use as ammunition by the firearm.