Just because unfired 3" shotshells will fit in the chamber doesn't mean that the gun is chambered for them, or that it's prudent/safe to fire them in it.
FWIW, shotguns chambered for a shorter shell, like a 2 3/4" are long enough to accept an unfire 3" shell because the 2 3/4" chamber has to be long enough to allow the shotshells' mouth crimp to unfold/open w/o obstructing the passage of the shot charge and raising pressures.
If a shell too long for the actual chambering (like a 3" in a 2 3/4" chamber) is fired, the unfolded crimp has nowhere to go in the chamber, and so lies in the tapered forcing cone between chamber and bore, which obstructs the passage of the shot column, raising pressures dramatically.
European shotshell barrels have to be proved & marked for their chambering - usually underneath the barrel flats in centermeters. A 3" chambered barrel will have a "70" mark, while shorter chambers will have marks like "67" or "65", besides the gauge marking.
Your shotgun looks like one of the many hundreds made by small family business' ( F.PEDRFTTI ) and/or guilds in the gun-making center of Italy, the Gardone Valley, aka Val Trompia.
IIRC, Brescia is the region - like Americans might refer to New England (except it's a smaller area, of course).
While some of the establishments made entire guns, many simply made only parts (like barrels or actions) with others fitting & assembling the guns.
Last edited by PetahW; January 25, 2010 at 11:59 AM.