That gun is a descendant of the 1917, a revolver designed in hurry-up mode by S&W when America was on the cusp of entering WWI. The 1911 in .45acp had been adopted by the military a few years back (obviously), but Colt was not tooled up to produce NEAR as many 1911's as the army wanted. Still, the .45 was the only round they had and wanted to use. So, S&W devised a flat metal clip that held three of the .45acp rounds in a 'half-moon', by gripping them around the narrow inleted base of the case, and which rested against the back of the cylinder, replacing the cartridge rim. Load two half-moons, and you've got a cylinder-full.
After the war, Remington-Peters produced a rimmed adaptation of the .45 acp for all the 1917's then in circulation, dubbed the .45 AutoRim (still available as brass for handloaders from Remington and Starline). That looks more like a traditional revolver cartridge, though an oddly fat, squat one.
With the rise of Bullseye competition, S&W made target variations of the 1917, the models of 1950 and 1955 (25-2). In 1988, this was revised to a stainless steel, 5" version called the 625 (subsequently revised in numerous versions and lengths, but still all 625's). These guns are the kings of fast-revolver competition, since the 'half-moon' clip was replaced with 'full-moons', which firmly hold 6 rounds in a circle for an incomparably fast revolver reload.
The gun you link to is a scandium-framed, titanium-cylindered version of the 625--hence, 325.
