Join Date: Apr 2019
Location: Southeastern Pennsylvania
Darkgael is right on the mark with his information. The only thing left to mention is that shotgun shell lengths are measured as the length of the unloaded shell. a 3" shell is only 3'' after it's fired. A 2 3/4" is only 2 3/4" after firing, etc.
That said, as Darkgael stated, you may well be shooting a 2.5" chambered gun. It may be stamped on the side of the barrel as to exactly what size chamber it has.