During WWI, the standard Model 1911 auto pistol could not be produced fast enough, so the Army got Colt and S&W to make revolvers chambered for the standard .45ACP cartridge. The army called both guns the Model 1917. S&W developed 3-round half moon clips to allow faster loading, but mainly to allow normal extraction with the rimless cartridges. The first 50,000 Colt revolvers had no shoulders in the chambers so the rounds would fall into the chamber without the clip. Later Colts and all S&Ws can be fired without the clips but, of course, the empty brass has to be extracted with the fingernail.
In the past few years, a "full moon" clip was developed which holds the entire cylinder capacity.
In the Model 1917 revolvers, the headspace is made larger to allow for the case rim plus the clip. A rimmed cartridge, the .45 Auto Rim, was developed with an extra thick rim so it can be fired without the clip.
A conventional .38 or .357 revolver can be modified to use clips for faster reloading, but most conversions will not then work without the clips due to excess headspace. There is one conversion, using special clips, which involves cutting away the cylinder but leaving enough metal at the chamber to support the case rim. I have seen these, but have not actually used one.
Jim