If, by "extra gadget under the barrel," you mean the locking block, there is one. It is visible in the picture that shows the slide with barrel installed and the slide without the barrel installed. The locking block and its track is what turns, and thus unlocks, the barrel as the barrel moves rearward during recoil.

The forward lugs (4 in the picture) hold the barrel to allow it to travel back with the slide until pressure safely drops, then the bottom lug (3) engages the track in the locking block which turns the barrel, unlocking the forward lugs (4) from the slide, allowing the slide to continue its rearward travel to extract, eject, and pick up the next cartridge from the magazine. Then, in normal fashion, the recoil spring (compressed), forces the slide back forward as it uncompresses, carrying the cartridge up the fixed ramp and into the chamber as the bottom lug (3) reverses direction in the locking block track, thereby rotating the barrel back into its position as it gets to its forward position, allowing the forward lugs (4) to lock into their recesses in the slide.