I forgot Smith 9mm guns. There are probably a few others out there, too. Don't think anyone but Ruger made interchangeable ones, though.
I never could understand why anyone in their right mind would buy one, other than the interchangeable cylinder ones that allowed cheaper ammo for practice.
Myron
How many peckers can a Pecker Checker check if a Pecker Checker could check peckers? (stolen from shootinurse)