[Alpo]

A 2 3/4 inch shell will fit fine in a 2 1/2 inch chamber. So that tells you nothing. The correct way to tell is with a chamber gauge. That will cost you about 80 bucks, so you may not want to go that way.

A cheaper way, if your local gunshop will let you, is to just bring in the barrels (that alleviates the worry about "loaded gun in the store") Drop a 3 1/2" shell in the chamber, and mark on the side of the shell how deep it goes (I just used a sharpie). Tnen measure from the bottom of the shell to the mark.

I say to use a 3 1/2 inch shell, because a 3" will fit in a 2 3/4 inch chamber. 3 1/2" won't.

Once you've measured the distance (and now know the length of your gun's chamber) just put the shell back in the box and put it back on the shelf. You haven't hurt it any - it's just got a magic marker line on the side of it.