Legal Notes

Law Italian law (in keeping with European agreements and directives) has always ignored these items, which are therefore permitted.
They are not subject to any regulations, do not have to be stamped by the Proof House, and do not have to bear distinctive marks.
They do not in any way fall under the concept of interchangeable barrels and therefore do not have to be registered.
Reducers are not part of the gun, but mere accessories (i.e., a thing having its own structural individuality, intended to supplement, vary or improve the use of something else that is already complete in itself).
To understand the difference from the interchangeable barrel, consider that the latter can be used only on a specific weapon model and sometimes only on a specific weapon; the reducer, on the other hand, can be used on an indefinite number of weapons as long as they are of the same caliber.
Those who possess an interchangeable barrel can always make up a whole weapon if they come into possession of the other parts (e.g., barrel and slide of a pistol); those who possess a reducer cannot use it unless they already have a functioning and complete weapon of their own.
If this interpretation is not adopted, scopes and pistol holsters should also be considered weapon parts!
Finally, it is clear that if some interpretive doubt could arise for reducer can ne (must they be submitted to the Proof House? Must they be registered?) no doubt can arise for reducer shells.
Since they are not weapon parts, but only accessories, they are free for sale and do not have to be reported.
Indeed, consider that those consisting of a smooth bore case can be made by anyone who knows how to use a drill and cutter.
Italian hunting law also ignores them, but they must be considered prohibited for hunting uses in Italy if they employ ammunition whose caliber is not permitted for hunting weapons.
On the other hand, they are allowed if they are in a permitted caliber (e.g., 6.35 cal. for pistol), unless, of course, the local hunting calendar prohibits the use of rifled guns.
My assertion that reducers are not parts of weapons or interchangeable barrels was upheld by the Court of Appeals of Venice in a ruling of 1-6-2001, confirming a ruling of the Court of Belluno, with the statement that “it must in fact be held that the mechanism in question constitutes a caliber reducer and not an interchangeable barrel; the reducer does not increase the potential for offense.”
Thus, in addition to establishing that it was not part of a weapon, it also ruled that it does not constitute alteration of a weapon to mount a reducer.
This is an obvious statement since no mechanics of the weapon are altered, which is a prerequisite for having an alteration in the case of power modification.