If the chamber is bigger than a 20 gauge, then is 14 gauge, if it is about the size of a .410 then it is 14MM, as far as I know there is no such animal as a 14 caliber per say, it is 14 something
. The only way you can tell for sure is to measure the chamber, we are just giving the possibilities. Only the person who has possession of the shotgun can make that determination