You can find info online at www.pmcammo.com
I think Briley makes tubes to fit their system (and I would recommend these), but no just any 12 ga. tube won't work.

Outdoorsmen, I'm not real surprised that their action is stiff, these seems to be the one thing that most Italian O/U's have in common. The rough bore doesn't bother me as I usually have my forcing cones polished anyway (unless they have a mirror finish from the factory, which is rare).

Gordon