The modular weapon system. The Eugene Stoner 63 system. A concept worthy and valid that for whatever reason never took off as it should have.
"Eugene Stoner pioneered the modular weapon system through his all-in-one Stoner 63 automatic series . . . The Stoner 63 utilized a common receiver core to which various feeds, barrels, shoulder stocks, and other components were attached to configure the weapon's in-the-field service . . . the weapon could take on various profiles to suit the mission need."
That Stoner 63 system the total package. A variety of weapons to be configured from one basic and common receiver.
See also this video the Stone 63 survival carbine with assembly as shown. This is how the process of assembly and task tailoring for mission was done.