A takedown pin system may be used for the processes of securing, semi-securing, and/or un-securing the rear connection points of firearm lower and upper receivers, for example, of an AR-15, with an option to maintain axial engagement of the pin to the receivers throughout two or more of the processes. An enhanced pin detent track allows pin rotation when axially-engaged in the receivers. A narrow pin body portion, for example, a recessed side surface portion or a narrow flange, cooperates with the pin hole and/or a slot in an upper receiver rear knuckle. Rotating the pin may locate the recess or flange to make room between the pin and the inner surface(s) of the upper receiver pin hole so the upper receiver can pivot slightly open from the lower receiver. A slot at the bottom of the rear knuckle hole may receive a flange of the takedown pin.