In 1956-1959 Bill toyed with the idea of making a lighter six shooter. Aluminum was used as a grip frame and cylinder. The cylinder had steel inserts. Since aluminum doesnt blue they were first anodized (known as the “tri color”) and baked paint. Total produced about 12,000 of which 4 variations exist. The latter had a steel cylinder as seen here.
It is of special note that the boxes they came in are usually worth as much or more than the gun to collectors. Unfortunately this one didnt come with one.