Beretta Silver Pigeon Pump Takedown

[Larryk19D]

I have a 1969 Silver Pigeon Pump. Can't seem to figure out how to get the barrel off. I got a copy of the "original" manual and as you would expect, just unscrew the nut on the end of the magazine tube. When I unscrew it, it is still held in place with something from inside the tube. This isn't mentioned in the manual. Not too many of these shotguns made, any help would be appreciated.

Thanks, Larry