Colt has not made a five shot revolver in over a hundred years that I recall.
A lightweight .38 Special Colt would be either a Cobra or an Agent. Six shot. Same size as Detective Special, but with aluminum frame. The early Cobra had full length grip straps, the Agents had shortened butts. Later all D frame Colts went to the short butt and the Cobra and Dick Special just had grips that wrapped under the butt to keep the standard length.