Going long, in .38 Rimless Smokeless!
Tweaking his own Colt Model 1900, John Browning coughed up a beefy longslide autoloader in .38 Automatic Colt Pistol, marked “.38 Rimless Smokeless” on the slide, to make sure the cartridge was easily differentiated from something that ran on black powder.
The result was the Colt M1902:
More in my column at Guns.com.