Father of the Magnum Cartridge
Ultimately, there is only one equation: Momentum = Mass x Velocity. When you talk about bullets, you talk about how much they weigh and how fast they're going. This allows various approaches to the same problem. You can have a small bullet traveling at a high velocity, or a big bullet moving much more slowly. And all the various combinations in between. Of course, you can also launch a big bullet at a high velocity, but you need a much bigger, stronger platform to do that, and since we're talking about handguns here we are faced with some real limitations.
Over the years, for reasons both technical and traditional, large caliber handguns used bullets from either the .36 or .45 caliber class - referring to the bullet diameter in inches. The .38 Colt, .38 Special and 9mm Parabellum are examples of .36 caliber class rounds, while the .45 Colt, .455 Webley and .45 ACP are common examples of the .45 class. Early handguns used black powder, which burned more slowly and was unable to develop significant chamber pressures. Therefore the lack of immense metallurgical strength in frames, cylinders and chambers was never an issue. You poured in a bunch of black powder and pushed a great big heavy bullet out the barrel in a cloud of gunsmoke. With the transition to smokeless powder in the late 19th century, it was suddenly possible to build much more powerful cartridges, and the metallurgists of the day struggled to keep up.
Elmer Keith was an old western legend, a hunter, outdoorsman, shooter and gunfighter. He was a deeply committed believer in the small fast bullet approach, and as firearms manufacturers began to build much stronger guns, he began loading the old .38 Colt to much higher velocities. The reason he could do this is he switched from the old 'heeled' type bullet that had a significant portion of its mass inside the brass case, to more modern bullet designs where the bullet was the same diameter as the inside of the case. This is why a .38 bullet actually measures .357" in diameter. These bullets left more room in the case for powder and have come to be known as "Keith" style bullets.
Throughout the 1920s, Keith experimented with hotter and faster loads in .38 revolvers. Eventually, his friends at Smith and Wesson bought in, and began production of the so-called "Magnum" revolvers in 1935. The .357 Magnum round, particularly in it's 125 grain jacketed hollowpoint loading (see? Bullets are way cooler than guns) was, and remains, the most effective handgun round for shooting people that has ever been designed. There are advocates who would argue instead for the .45 ACP - and this is perhaps the greatest "religious" argument in the handgun community - but the numbers, particularly those compiled by Evan Marshall in his seminal studies on handgun stopping power, bear out the undeniable truth. Keith went on to do the same thing with the .45 caliber class - the infamous .44 Magnum - and an intermediate 10mm Magnum chambering called .41 Magnum - but with its combination of usability, accuracy and deadly terminal ballistics the .357 has always been the queen of combat handguns.
I carried .357s, primarily 4" Smith & Wesson Model 13s, 19s and 66s for decades. I never felt like I might be outgunned, and one night when things got real dark and chaotic and I had my .45 Star PD instead I was deeply furious with myself for putting myself in that position. I recognize that the world has embraced the .40 Smith auto, and nobody born after 1980 will ever appreciate the revolver, but that is silly and shortsighted. They talk endlessly about magazine capacity, speed of reload and firepower, but as my dad used to say, "if you can't get it done with six rounds you never had a chance anyway".