To be absolutely sure, have a gunsmith measure it.
read the link you had posted before the edit and I got the same lenth as you did, I called to see if my grandpa could still remember what size he had used and he happened to still have some 2.5" shells, so thats what i will use untill I ever need a gunsmith then I may take it also and ge tthem to check it out.
... he happened to still have some 2.5" shells, so thats what i will use untill I ever need a gunsmith then I may take it also and ge tthem to check it out.



























