This Model 25-2 dual-cylinder revolver may be something along these lines--Roy says it won't letter, but the case insert is very obviously die-cut for the .45 Colt cylinder, which is the short version from the Model 25-3 Commemorative.

It may have been made as a "clean-up" gun to use leftover 25-3 cylinders, but who knows?

I have never bothered to letter it, based upon what Roy told me, but maybe I should.