Are you talking about the mag cap ??
Like this ???
http://www.amazon.ca/Uncle-Mikes-Detachable-Mossberg-12-Gauge/dp/B0013R6CYC
Where are you at in Montreal?.... I work on the west island and have a few kicking around.....
Thy can be changed from barrel to barrel no problem thy just screw in ..DutchIf you have 2 mag caps can you not interchange them . Or is the cap barrel specific ?



























