The 645 its single action fraternal twin, the 745 were the first .45 ACP semi-auto pistols S&W ever made. The 645 was not long lived as Smith got bought out by Thompkins who insisted they streamline manufacturing and design. The 4506 came along and the large frame pistol market was never the same.
In life, strive to take the high road....It offers a better field of fire.
"Robo is right" Fuzzball