hello
It has been a long time since I removed a barrel !!!!.
It seems that with all the undercover removed, you should find under the housing of the barrel, a square piece of metal which is locked by a bare -head screw ( a kind of riveted).
With a screwdriver and a hammer, gently unscrew the bolt, and -plug of ignition disconnected -you can release the complete lock (photo).
then push the spring,in a tiny hole (photo)...
and this is it !!!!