The M48 is a K-frame .22 Mag that came with 4",6",or 8 3/8" barrels. It was manufactured from 1959 to 1986. Some were offered with a "conversion kit", or .22 lr cylinder and yoke. They had pinned barrels and recessed chambers, as the earlier Smiths all did. (pre '82) Some other features included a top rib on the barrel, smooth trigger, semi-target hammer, and a Patridge front sight on the 6" and 8 3/8" barrels. The Nickel plated models were never cataloged, but there are some out there, if you can find them. In 1978, 135 were made without the model number marked on the gun. Why? I don't know, but I bet someone will pay a lot for one! I hope that this has been helpful.