I owned one of those many years ago. It shot ok and was rather well made, but I never got used to its non-standard conception. If I remember well, there is a stud between the barrels that also serves as the hinge pin on wich the barrels turn. This stud has to be DEPRESSED, after wich the barrels can be inserted into the receiver.(not without difficulty, you will have to experiment a little to find the right 'angle of entry'). Hope this will be of help.
Greetings,
Livinus