In 1955 Hamilton introduced the 22 jewel 770 movement. This 12/0 sized movement is highly regarded as the best movement that Hamilton ever produced. It continued to be manufactured in Lancaster PA until 1969.
From 1958 through 1961, Hamilton produced the Chapman, featuring the 770 movement. It was part of the "Medallion" line up. Hamilton also had a "Masterpiece" line of solid gold watches and a "Medalist"series of gold filled watches. I imagine the Medallion series was a step up from the Medalist series. It's hard to say though, as Medalist watches were still a premium level versus Hamilton's other less expensive rolled gold plated models.
Here's a Chapman that I received as a wreck and was able to restore to it's former glory.
As received, it had lost it's crystal and had developed a serious case of "dial rash". In addition, the hands were very corroded and needed to be replaced (although they can be refinished too).
With the case nicely polished, a new set of hands, a nice glass crystal installed and professionally refinished dial - this Chapman was a thing of beauty.